www.digitalmars.com         C & C++   DMDScript  

D - Arrays, Slices, Cases

reply Karl Bochert <kbochert ix.netcom.com> writes:
Having too much time on my hands, I submit the following
summary of my viewpoint.  At the very least it shows how I
will rationalize the method that D uses.

I would welcome any other rationale that would make D's
choices seem more natural.

(After 20 yrs of C, I still have fencepost problems! :-)

Concerning Arrays, slices, and cases.

1) Ordinal Arrays
     Arrays are ordered set of elements accessed by their position
     in the set.
     An array with N elements has a first element and an
     N'th element.
     A slice of the entire array is arr[1..N].
     A slice excluding the ends is arr[2..N-1].

  end-inclusion:
      a slice can be thought of as the result of a procedure
      that (somehow) extracts the range, similar to:
          result = slice (&arr[start], &arr[end]);
      Obviously, end is included.

      a slice can be thought of as the result of a loop that
	  'extracts' elements of the array, similar to:
         for (i = start, i <= end; ++i)  result[1+i-start] = arr[i];
      Obviously, like the for loop,  'end' is included.
	  Cases are also end-inclusive:
      case [1]:
      case [2 to 4]:
      case [5]:

  end-exclusion:
      Why would anyone do that?

-----------

2) Cardinal Arrays
    Arrays are chunks of storage accessed by the offset from
    their start.
    An array with N elements has a zero'th element and an N-1'th
    element.
    A slice of the entire array is arr[0..N-1].

    end-inclusion:
      A slice excluding the ends is arr[1..N-1].
      a slice can be thought of as the result of a procedure
      that (somehow) extracts the range, similar to:
          result = slice (&arr[start], &arr[end]);
      Obviously, end is included.
	  Cases are also end-inclusive:
      case [1]:
      case [2 to 4]:
      case [5]:
	  

    end-exclusion:
      A slice excluding the ends is arr[1..N-2].
      a slice can be thought of as the result of a loop that
      'extracts' elements of the array, similar to:
         for (i = start, i < end; ++i) result[i-start] = arr[i];
      Obviously, like the for loop, end is excluded.
      Cases are also end-exclusive:
         case [1]:
         case [2 to 5]:
         case [5]:
      Cases are end-inclusive (different than slices)
         case [1]:
         case [2 to 4]:
         case [5]:


D is:
  Cardinal arrays, end-exclusive, case-inclusive?

I am for:
  Ordinal arrays, end-inclusive, case-inclusive.
  simpler and more consistant. 

Karl Bochert
Feb 21 2002
parent reply not here <not.known this.address.com> writes:
On Fri, 22 Feb 2002 00:43:28 GMT, Karl Bochert <kbochert ix.netcom.com> wrote:

 
 Having too much time on my hands, I submit the following
 summary of my viewpoint.  At the very least it shows how I
 will rationalize the method that D uses.
 


[big snip]


 
 D is:
   Cardinal arrays, end-exclusive, case-inclusive?
 
 I am for:
   Ordinal arrays, end-inclusive, case-inclusive.
   simpler and more consistant. 


Hi Karl,
whether one uses either a index or an offset to reference an array element, is
often influenced by 
what we have been exposed to already. However, I'd like to approach the issue
in a different manner.

To me an 'index' is 1-based and is a normal way that people think about
enumerated elements. If you 
go up to somebody with a list of items and asked them to number them, the
person would normally 
start with the number 1.

An 'offset' is 0-based and is the normal way that computers get access to
memory. Addr + offset 
gives another address - the start of the element in question.

I believe that programming languages have a primary aim of helping people
describe their algorithms. 
In other words, programming languages are for people and not computers - that's
why we have 
compilers. So, I would hold that 1-based array referencing is the normal way
for people to describe 
what they are trying to do.

Furthermore, an index has the connotation that the entire element is being
referenced, whereas an 
offset is better thought of referencing the start of an element. Thus a slice
reference of say 


whole of each of these elements. The fact that the length of this slice is 3 is
obvious because all 
of the elements are being referenced. 

If we were using offsets in slice notation, then [2..4] would be saying that
the slice starts from 



not how people 
normally view the world.

I vote with Karl on this one.  Besides, calculating the length of an index
notation slice is not 
beyond us, especially if we can do "  myArray[x..y].length "

Now consider the way we might remove an element from a dynamic array.

Given that 'pos' references the element to be removed...

using Index Notation
   A1 = A1[1..pos-1] ~ A1[pos+1 .. A1.length]

using Offset Notation
   A1 = A1[0..pos] ~ A1[pos+1 .. A1.length-1]

Not a lot of difference really. Personally, I find that the index notation is
more clearly telling 
the reader that I am trying to exclude the 'pos' element but include everything
else.

-------
cheers.
Feb 21 2002
parent reply Karl Bochert <kbochert ix.netcom.com> writes:
 Hi Karl,
 ...
 To me an 'index' is 1-based and is a normal way that people think about
enumerated elements. If you 
 go up to somebody with a list of items and asked them to number them, the
person would normally 
 start with the number 1.
 
 An 'offset' is 0-based and is the normal way that computers get access to
memory. Addr + offset 
 gives another address - the start of the element in question.
 


Exactly - its an issue of computer arrays vs. human arrays.


 
 Furthermore, an index has the connotation that the entire element is being
 referenced, whereas an  offset is better thought of referencing the
 start of an element. 
 


Hadn't occured to me, but you are right.


 ...
using Index Notation
   A1 = A1[1..pos-1] ~ A1[pos+1 .. A1.length]

using Offset Notation
   A1 = A1[0..pos] ~ A1[pos+1 .. A1.length-1]


Didn't you get that wrong?

using Offset Notation (exclusive)
    A1 = A1[0..pos] ~ A1[pos+1 .. A1.length]

using Offset Notation (inclusive)
    A1 = A1[0..pos-1] ~ A1[pos+1 .. A1.length-1]

(I think thats right -- I had to draw little boxes
on a sheet of graph paper)

 I have this sneaky feeling that the reason D uses offsets instead of
indexes is to be backward- compatible with C, and therefore
more familiar.


Karl Bochert
Feb 21 2002
parent reply not here <not.known this.address.com> writes:
On Fri, 22 Feb 2002 05:49:50 GMT, Karl Bochert <kbochert ix.netcom.com> wrote:

 Hi Karl,
 ...
 To me an 'index' is 1-based and is a normal way that people think about
enumerated elements. If 




you 

 go up to somebody with a list of items and asked them to number them, the
person would normally 
 start with the number 1.
 
 An 'offset' is 0-based and is the normal way that computers get access to
memory. Addr + offset 
 gives another address - the start of the element in question.
 


 Exactly - its an issue of computer arrays vs. human arrays.
 


I really think that too many language designers forget that its people that
have to actually use 
them, and not computers. The "user-interface" for most programming languages is
sub-optimal. Often 
the language encourages hard-to-comprehend syntax thus making it easier for
people to make mistakes.


 ...
using Index Notation
   A1 = A1[1..pos-1] ~ A1[pos+1 .. A1.length]

using Offset Notation
   A1 = A1[0..pos] ~ A1[pos+1 .. A1.length-1]


 
 Didn't you get that wrong?
 
 using Offset Notation (exclusive)
     A1 = A1[0..pos] ~ A1[pos+1 .. A1.length]
 
 using Offset Notation (inclusive)
     A1 = A1[0..pos-1] ~ A1[pos+1 .. A1.length-1]
 
 (I think thats right -- I had to draw little boxes
 on a sheet of graph paper)


Ooops. You are right. I did get the 'index' code wrong. That might be example
of its inherent non-
user-friendly interface ;-)

    A1 = A1[0..pos] ~ A1[pos+1 .. A1.length]

is what I should have coded. To the average person, knowing the 'pos' refers to
the element being 
removed, this code looks wrong as it seems to be including A1[pos]!




  I have this sneaky feeling that the reason D uses offsets instead of
 indexes is to be backward- compatible with C, and therefore
 more familiar.
 


More familar to whom? C/C++ coders? One would have hoped that D might be used
as a replacement for 
C/C++ and thus newbies can learn a "better" language and not have to be
backward compatible. Also, 
reading the D Overview we find under the things to drop from C/C++ 

"C source code compatibility. Extensions to C that maintain source compatiblity
have already been 
done (C++ and ObjectiveC). Further work in this	area is hampered by so much
legacy code it is 
unlikely that significant improvements can be made." 

----
cheers.
Feb 21 2002
next sibling parent reply "Sean L. Palmer" <spalmer iname.com> writes:
"not here" <not.known this.address.com> wrote in message
news:1103_1014364009 news.digitalmars.com...

 On Fri, 22 Feb 2002 05:49:50 GMT, Karl Bochert <kbochert ix.netcom.com>


wrote:

 To me an 'index' is 1-based and is a normal way that people think






about enumerated elements. If

 you

 go up to somebody with a list of items and asked them to number them,






the person would normally

 start with the number 1.

 An 'offset' is 0-based and is the normal way that computers get access






to memory. Addr + offset

 gives another address - the start of the element in question.


 Exactly - its an issue of computer arrays vs. human arrays.





 I really think that too many language designers forget that its people


that have to actually use

 them, and not computers. The "user-interface" for most programming


languages is sub-optimal. Often

 the language encourages hard-to-comprehend syntax thus making it easier


for people to make mistakes.

I don't know what planet you guys are from... go use BASIC or something if
you want arrays that start at position 1 instead of 0.

Computer arrays start at 0.  Every programmer needs to learn this right
away.  It's very fundamental, and trying to "humanize" it just results in a
language that requires suboptimal code generation.

I personally think they should teach people about zero earlier on in school,
then we wouldn't have this problem.  How would you like that?  ;)

Sean
Feb 22 2002
next sibling parent "Pavel Minayev" <evilone omen.ru> writes:
"Sean L. Palmer" <spalmer iname.com> wrote in message
news:a552bk$17v$1 digitaldaemon.com...


 I personally think they should teach people about zero earlier on in


school,

 then we wouldn't have this problem.  How would you like that?  ;)


Great idea! So, I have two cars, the zeroeth is red and the first is blue =)
Feb 22 2002
prev sibling parent not here <not.here this.address.com> writes:
On Fri, 22 Feb 2002 01:18:54 -0800, "Sean L. Palmer" <spalmer iname.com> wrote:

 
 I don't know what planet you guys are from... go use BASIC or something if
 you want arrays that start at position 1 instead of 0.
 
 Computer arrays start at 0.  Every programmer needs to learn this right
 away.  It's very fundamental, and trying to "humanize" it just results in a
 language that requires suboptimal code generation.
 
 I personally think they should teach people about zero earlier on in school,
 then we wouldn't have this problem.  How would you like that?  ;)


This sounds a lot like "Well thank you, Ma'am, but quite frankly, that's not
how we do things around these parts".

I would have thought that with D, we have a chance to break free of the
computer-centric way of doing things and instead design a language that makes
life easier for coders at every possible chance. If people all 
around the world, in all cultures (except it seems, vetern coders), count off
things starting with one, why should we have to "retrain" them to start
thinking as if they are a computer.

Yes, I know that computer arrays start at 0. Just like my high school ruler


If one is truely concerned with suboptimal code generation, we would all be
still creating hand-crafted assembler (or even machine code) programs. All we
are talking about here is sometimes generating a "subtract 
one"  opcode or similar, and todays, let alone tomorrow's, computers are very,
very fast.  

Isn't a compiler a tool? A tool for people to use? To make our lives easier? So
let our compilers take what is normal for people and convert it for computer
usage, rather than having the language make people 
convert what is normal for them into computer-ese.

-------
cheers.
Feb 22 2002
prev sibling parent reply "Pavel Minayev" <evilone omen.ru> writes:
     A1 = A1[0..pos] ~ A1[pos+1 .. A1.length]

 is what I should have coded. To the average person, knowing the 'pos'


refers to the element being

 removed, this code looks wrong as it seems to be including A1[pos]!





 More familar to whom? C/C++ coders? One would have hoped that D might be


used as a replacement for

 C/C++ and thus newbies can learn a "better" language and not have to be


backward compatible. Also,

 reading the D Overview we find under the things to drop from C/C++


I believe Walter said that D is not a language for the beginners. BASIC,
or even Pascal would be better for this purpose. D is a practical language
for practical programmers, and I don't think it's the best idea to
sacrifice speed to gain such a subtle simplicity, IMO...


 "C source code compatibility. Extensions to C that maintain source


compatiblity have already been

 done (C++ and ObjectiveC). Further work in this area is hampered by so


much legacy code it is

 unlikely that significant improvements can be made."


"compatibility" means ability to compile code from that language.
This is what D is not for. But there are many programmers that know

those people expect to find a common environment to start coding
quick, without having to learn everything from scratch. Arrays are
indexed from 0, every C programmer should remember that better than
his own name - why disappoint them? 0-based indexing is a tradition
too old to change it - it's better to live with it, especially
since it's not hard to get used to it.
Feb 22 2002
next sibling parent reply not here <not.here this.address.com> writes:
On Fri, 22 Feb 2002 16:09:36 +0300, "Pavel Minayev" <evilone omen.ru> wrote:

     A1 = A1[0..pos] ~ A1[pos+1 .. A1.length]

 is what I should have coded. To the average person, knowing the 'pos'


 refers to the element being

 removed, this code looks wrong as it seems to be including A1[pos]!


 



Should I infer then that the average D programmer is always going to be an

future of D? Can we not expect COBOL coders to come 
over the fence? If not, why not?


 More familar to whom? C/C++ coders? One would have hoped that D might be


 used as a replacement for

 C/C++ and thus newbies can learn a "better" language and not have to be


 backward compatible. Also,

 reading the D Overview we find under the things to drop from C/C++


 
 I believe Walter said that D is not a language for the beginners. BASIC,
 or even Pascal would be better for this purpose. 


I assume that Walter is referring to people who are just learning to program. I
would have thought that the fewer new things that people have to learn, the
sooner they can become productive. If this is so, then it 
would appear than a design goal for D is to assume new comers to D will be
existing C/etc coders so they don't have to learn too many new things. Oh well,
maybe we are condemed to repeat history.


 D is a practical language
 for practical programmers, 


.meaning that Basic and Pascal are NOT practical languages, and their users are
NOT practical? Ummm. Sounds a little xenophobic to me.


 and I don't think it's the best idea to
 sacrifice speed to gain such a subtle simplicity, IMO...


Why is that we spend hours of coding time to optimise a few micro-seconds into
a program? We no longer live in the age when computer time is more expensive
than people time. It seems you are willing to sacrifice 
coders time rather than computer time. I don't think it's the best idea to
sacrifice coding speed, IMO.


 "C source code compatibility. Extensions to C that maintain source


 compatiblity have already been

 done (C++ and ObjectiveC). Further work in this area is hampered by so


 much legacy code it is

 unlikely that significant improvements can be made."


 
 "compatibility" means ability to compile code from that language.
 This is what D is not for. But there are many programmers that know

 those people expect to find a common environment to start coding
 quick, without having to learn everything from scratch. Arrays are
 indexed from 0, every C programmer should remember that better than
 his own name - why disappoint them? 


Heaven forbid that we should try to retrain C coders! Everyone knows that we
are sacrosanct and must be protected.
Every good C programmer knows how useful the macro preprocessor is (oops,
that's not in D is it?)
Every good C++ programmer knows how useful multiple inheritance can be (ooops,
that not in D is it?)

that's not in D is it?)
Every C programmer can type #include files in their sleep (ooops, that's not in
D is it?)

Yes I know these are a little unfair. But what I'm trying to get across is that
D will already force C coders to learn/unlearn things. So why not have 1-based
indexes, just like we use in the real world.


 0-based indexing is a tradition
 too old to change it - it's better to live with it, especially
 since it's not hard to get used to it.


Hey we got tradition! You can't mess that baby. Sure it makes things a bit
harder but you'll soon get used to that.

Is this the same as saying "We can't do that new thing because its not what we
currently do"? 

I could just as equally say "1-based indexing is not hard to get used to,
seeing you already do it everywhere else except when you are thinking like a
computer."

-----
cheers
Feb 22 2002
next sibling parent reply "Pavel Minayev" <evilone omen.ru> writes:
"not here" <not.here this.address.com> wrote in message
news:1104_1014393359 news.digitalmars.com...


 Should I infer then that the average D programmer is always going to be an



the future of D?

Definitely not. However, the most popular language nowadays is C++, so
C-centric
model seems most appropriate to me here.


 .meaning that Basic and Pascal are NOT practical languages, and their


users are NOT practical? Ummm. Sounds a little xenophobic to me.

Not really. It's just that C/C++ proves to be better in such cases. So
should D.


 Why is that we spend hours of coding time to optimise a few micro-seconds


into a program? We no longer live in the age when computer time is more
expensive than people time. It seems you are willing to sacrifice

 coders time rather than computer time. I don't think it's the best idea to


sacrifice coding speed, IMO.

There is no "sacrifice" in coding speed with 0-based indexing. Nothing
you can't get used to, and, in fact, many programmers over the world
are already. On other hand, that microsecond can cost you 20fps drop
when writing a game which iterates through 100000 objects in a loop...


 Every good C programmer knows how useful the macro preprocessor is (oops,


that's not in D is it?)

Preprocessor thing had been discussed many times and there are _very_
serious reasons to ban it. After all, if you really need one, you
can always use an external program. Otherwise, most uses of preprocessor
in C are covered by constants, inline functions, and version/debug
statements in D.


 Every good C++ programmer knows how useful multiple inheritance can be


(ooops, that not in D is it?)

The latest discussion on the topic in this group shows that, in fact, most
C++
programmers use MI rarely or don't use it at all.





(ooops, that's not in D is it?)

Namespaces ARE good. And they are present in D - implicitly, each module is
a namespace. Don't forget about packages as well. And the fact that each
enum has its own namespace speaks for itself.


 Every C programmer can type #include files in their sleep (ooops, that's


not in D is it?)

    import c.stdio;


 Yes I know these are a little unfair. But what I'm trying to get across is


that D will already force C coders to learn/unlearn things. So why not have
1-based indexes, just like we use in the real world.

Even in the real world, indices aren't always 1-based.
Then again, with 1-based arrays, you can only have 2^32-1 elements,
while with 0-based you get the whole 2^32! Just think of all the
benefits this gives! =)


 Hey we got tradition! You can't mess that baby. Sure it makes things a bit


harder but you'll soon get used to that.

"Tradition" isn't something you should get used to. It's something
that _most_ people got used two.


 Is this the same as saying "We can't do that new thing because its not


what we currently do"?

Almost. Just because it seems impractical.


 I could just as equally say "1-based indexing is not hard to get used to,


seeing you already do it everywhere else except when you are thinking like a
computer."

Well, mathematicians don't use it.
Also, I understand why a user shouldn't think like a computer. But
why not programmer? Memory is indexed from 0, nothing you can do
with it. So are all that assembler opcodes that your program ends
up being, anyhow. You write programs for computers, not for men,
after all...
Feb 22 2002
parent Karl Bochert <kbochert ix.netcom.com> writes:
On Fri, 22 Feb 2002 21:27:16 +0300, "Pavel Minayev" <evilone omen.ru> wrote:

 

 There is no "sacrifice" in coding speed with 0-based indexing.


Maybe not for you! 


 ...
 Nothing
 you can't get used to, and, in fact, many programmers over the world
 are already. On other hand, that microsecond can cost you 20fps drop
 when writing a game which iterates through 100000 objects in a loop...


Actually the instruction time for an add is more like 1 ns. these days,
especially on computers where speed is a concern.
The cpu has multiple execution units, so the add would frequently be done
in parallel with other instructions, costing 0 time.
The +1 will often be combined with another  constant costing 0 time.
Many assembly instructions used for array access use an addressing mode
that adds a constant whether it is needed or not, again 0 time.

Finally there is the issue of how often the +1 comes up in the first place.
arr[2]   -- no +1
arr[x]   -- no +1 unless the programmer has stored the wrong thing in x
Of course you run into a problem if you pass a cardinal to something that
expects an ordinal!

An interesting point:
Addressing arrays with cardinals implies the existence of an element at [-1].
There are no negative ordinals!


 
 Even in the real world, indices aren't always 1-based.


The obvious example is computer hardware, which uses cardinal
indexes. 


 Then again, with 1-based arrays, you can only have 2^32-1 elements,
 while with 0-based you get the whole 2^32! Just think of all the
 benefits this gives! =)


Actually, I think cardinal arrays have (theorectically) half as many
indexes. Unless you count (shudder) negative indexes.
I suppose implementation issues would limit ordinal arrays
though.
 

 Is this the same as saying "We can't do that new thing because its not


 what we currently do"?
 
 Almost. Just because it seems impractical.


The only thing about it that is even mildly difficult is that D is already
written using cardinal arrays ( And that is a killer!)


 
 Well, mathematicians don't use it.
 Also, I understand why a user shouldn't think like a computer. But
 why not programmer? Memory is indexed from 0, nothing you can do
 with it. So are all that assembler opcodes that your program ends
 up being, anyhow.


The program actually ends up being binary -- I would like to make as
few concessions as possible to that unfortunate fact.


 You write programs for computers, not for men,  after all...


I write programs for 2 readers: compilers, and humans (If you can call
programmers that :-)
The great majority of my programming time is spent trying to satisfy the humans.
Feb 22 2002
prev sibling parent reply Russell Borogove <kaleja estarcion.com> writes:
not here wrote:

 Heaven forbid that we should try to retrain C coders! 
 Everyone knows that we are sacrosanct and must be protected.
 Every good C programmer knows how useful the macro 
 preprocessor is (oops, that's not in D is it?)
 Every good C++ programmer knows how useful multiple 
 inheritance can be (ooops, that not in D is it?)

 can be (ooops, that's not in D is it?)
 Every C programmer can type #include files in their sleep 
 (ooops, that's not in D is it?)
 
 Yes I know these are a little unfair. But what I'm trying to 
 get across is that D will already force C coders to learn/
 unlearn things. So why not have 1-based indexes, just like
 we use in the real world.


I don't see the problem as being one of tradition -- as you point
out, Walter has dispensed with a number of C/C++ traditions -- but
of practicality. The changes you describe above are wholesale
removals of features that the compiler can slap you for very
quickly if you forget about. Trying to use the preprocessor in
D clearly won't lead to subtle bugs; the compiler will scream and
the typical programmer will very quickly adapt.

Changing the index base will create subtle bugs, because code
that would compile in C or C++ will still frequently compile in
what I'll call D-1 (D with 1-based arrays), but change its meaning.
That scares me. The most common error, of course, will be accessing
the zeroeth element of a 1-based array, which should throw an
exception, but how about the following code:

   void parse_command_line_option( char[] option )
   {
      switch (option[1]) // switch on the chracter after the '-'
      {
         case 'x': do_option_x(); break;
         case 'y': do_option_y(); break;
         default: printf("undefined option\n"); break;
      }
   }

The comment is correct for C/C++, but in D-1 the comment is
misleading and both "-x" and "-y" yield an undefined option
message.

-RB
Feb 22 2002
parent reply "Walter" <walter digitalmars.com> writes:
"Russell Borogove" <kaleja estarcion.com> wrote in message
news:3C76928A.8090508 estarcion.com...

 I don't see the problem as being one of tradition -- as you point
 out, Walter has dispensed with a number of C/C++ traditions -- but
 of practicality. The changes you describe above are wholesale
 removals of features that the compiler can slap you for very
 quickly if you forget about. Trying to use the preprocessor in
 D clearly won't lead to subtle bugs; the compiler will scream and
 the typical programmer will very quickly adapt.

 Changing the index base will create subtle bugs, because code
 that would compile in C or C++ will still frequently compile in
 what I'll call D-1 (D with 1-based arrays), but change its meaning.
 That scares me. The most common error, of course, will be accessing
 the zeroeth element of a 1-based array, which should throw an
 exception, but how about the following code:


And I want to emphasize this is an important point. D tries hard to avoid
having incompatibilities with C that will subtly break things. 1 based
arrays would do that. Another way to really mess people up would be to
change the operator precedence. Since D is meant to appeal to C and C++
programmers, I feel it would be a mistake to change those things, regardless
of how meritorious those changes are when viewed outside of the context of C
familiarity.

I've done some conversions of a few thousand line programs from C++ to D,
and it's bad enough finding and fixing all the dependencies on 0 terminated
strings. That turns out to be more work than I'd anticipated.
Feb 22 2002
next sibling parent "not here" <not.here this.address.com> writes:
"Walter" <walter digitalmars.com> wrote in message
news:a56tc2$1534$1 digitaldaemon.com...

 And I want to emphasize this is an important point. D tries hard to avoid
 having incompatibilities with C that will subtly break things. 1 based
 arrays would do that. Another way to really mess people up would be to
 change the operator precedence. Since D is meant to appeal to C and C++
 programmers, I feel it would be a mistake to change those things,


regardless

 of how meritorious those changes are when viewed outside of the context of


C

 familiarity.

 I've done some conversions of a few thousand line programs from C++ to D,
 and it's bad enough finding and fixing all the dependencies on 0


terminated

 strings. That turns out to be more work than I'd anticipated.


Thanks for this explanation, Walter. I now have a better understanding of
your goals for D. I wish you and your endevours well. I think you are off to
a good start.

Goodbye.
Feb 22 2002
prev sibling parent reply Karl Bochert <kbochert ix.netcom.com> writes:
 
 And I want to emphasize this is an important point. D tries hard to avoid
 having incompatibilities with C that will subtly break things. 1 based
 arrays would do that. Another way to really mess people up would be to
 change the operator precedence. Since D is meant to appeal to C and C++
 programmers, I feel it would be a mistake to change those things, regardless
 of how meritorious those changes are when viewed outside of the context of C
 familiarity.


So while ordinal arrays might be more technically correct, D would be less
successful with them. However annoying that is, I'm sure you're right.



 
 I've done some conversions of a few thousand line programs from C++ to D,
 and it's bad enough finding and fixing all the dependencies on 0 terminated
 strings. That turns out to be more work than I'd anticipated.
 


0-terminated strings today; 0-terminated arrays tomorrow. (maybe in 'E').

 Karl
Feb 22 2002
parent reply "Walter" <walter digitalmars.com> writes:
"Karl Bochert" <kbochert ix.netcom.com> wrote in message
news:1104_1014441056 bose...

 So while ordinal arrays might be more technically correct, D would be less
 successful with them. However annoying that is, I'm sure you're right.


Language design is inevitably going to be an uneasy alliance of
contradictory goals <g>. It's like designing a house - to make a bigger
closet, you have to shrink the bedroom.
Feb 22 2002
parent reply Barry Pederson <barryp yahoo.com> writes:
I've been following this debate about slices and cases with some interest.  As 
a Python programmer, I'm rooting for end-exclusiveness in slices - it's the 
way Python handles slices, and seems to work very well in practice.  If D 
sticks with that, then I think there'll be a lot of Python programmers who 
will be able to make use of it very comfortably.

Another Python-ish thing that might be worth considering would be support for 
negative array indexes.  For example:

    foo[-1]  is the last element of array foo
    foo[-2]  is the second-to-last element of array foo

then with slices

    foo[-2..] would be the last two elements of foo
    foo[1..-1] would be a copy of foo, except for the first and last elements

implementation should be pretty simple, for any index < 0, such as: foo[-n], 
the compiler would just treat it like: foo[foo.length - n]

CASES
----------

When it comes to case-ranges though, I agree that end-exclusiveness would be a 
weird PITA.  Perhaps the thing to do is decide that case-ranges and 
array-slices will be different things, and go ahead and use different syntaxes.

To steal from Python again, perhaps use a colon for array slicing (foo[1:-1]) 
and keep '..' for case-ranges (which seems pretty natural).

This would also kind of make sense if you also supported Python-style negative 
array indexes, since negative numbers in case-ranges would presumably have a 
completely different meaning.

     Barry
Feb 23 2002
parent "Walter" <walter digitalmars.com> writes:
"Barry Pederson" <barryp yahoo.com> wrote in message
news:3C77CFDD.2050404 yahoo.com...

 I've been following this debate about slices and cases with some interest.


As

 a Python programmer, I'm rooting for end-exclusiveness in slices - it's


the

 way Python handles slices, and seems to work very well in practice.  If D
 sticks with that, then I think there'll be a lot of Python programmers who
 will be able to make use of it very comfortably.

 Another Python-ish thing that might be worth considering would be support


for

 negative array indexes.  For example:

     foo[-1]  is the last element of array foo
     foo[-2]  is the second-to-last element of array foo

 then with slices

     foo[-2..] would be the last two elements of foo
     foo[1..-1] would be a copy of foo, except for the first and last


elements

 implementation should be pretty simple, for any index < 0, such as:


foo[-n],

 the compiler would just treat it like: foo[foo.length - n]


While this is a great idea, it suffers from a serious problem - the compiler
will have to insert a runtime check for negative indices whenever the index
expression is not a constant. This will be too much overhead.



 CASES
 ----------

 When it comes to case-ranges though, I agree that end-exclusiveness would


be a

 weird PITA.  Perhaps the thing to do is decide that case-ranges and
 array-slices will be different things, and go ahead and use different


syntaxes.

 To steal from Python again, perhaps use a colon for array slicing


(foo[1:-1])

 and keep '..' for case-ranges (which seems pretty natural).

 This would also kind of make sense if you also supported Python-style


negative

 array indexes, since negative numbers in case-ranges would presumably have


a

 completely different meaning.


Yes, using a different syntax may be the best solution.
Feb 23 2002
prev sibling parent reply "Roberto Mariottini" <rmariottini lycosmail.com> writes:
"Pavel Minayev" <evilone omen.ru> ha scritto nel messaggio
news:a55g08$7e8$1 digitaldaemon.com...

     A1 = A1[0..pos] ~ A1[pos+1 .. A1.length]

 is what I should have coded. To the average person, knowing the 'pos'


 refers to the element being

 removed, this code looks wrong as it seems to be including A1[pos]!





So I'm not an "average"  C/C++/Java programmer, therefore I use them only
since 1991/93/96.
I know how slicing currently works in D, but I had to double check to
understand.

[...]

 But there are many programmers that know

 those people expect to find a common environment to start coding
 quick, without having to learn everything from scratch. Arrays are
 indexed from 0, every C programmer should remember that better than
 his own name - why disappoint them? 0-based indexing is a tradition
 too old to change it - it's better to live with it, especially
 since it's not hard to get used to it.


I always wondered why C and derivatives don't have a way to define a start
index like Pascal does. To me it seems better to leave to the compiler the
task
to subtract the start index from the actual index. In C you write:

int occurrencies['Z'-'A'];
for (i = 0; i < size; ++i)
{
    ++occurrencies[s[i]-'A'];
}

Here the task to subtract 'A' to every indexing is left to the programmer.

Maybe the compiler could live with an optional initial index to subtract
every time
the array is accessed.

Ciao
Feb 22 2002
parent reply "Pavel Minayev" <evilone omen.ru> writes:
"Roberto Mariottini" <rmariottini lycosmail.com> wrote in message
news:a55s13$1c8a$1 digitaldaemon.com...


 So I'm not an "average"  C/C++/Java programmer, therefore I use them only
 since 1991/93/96.
 I know how slicing currently works in D, but I had to double check to
 understand.


End-exclusive slicing _is_ an issue, definitely. But we were talking about
0-based indexing.


 I always wondered why C and derivatives don't have a way to define a start
 index like Pascal does. To me it seems better to leave to the compiler the
 task
 to subtract the start index from the actual index. In C you write:

 int occurrencies['Z'-'A'];
 for (i = 0; i < size; ++i)
 {
     ++occurrencies[s[i]-'A'];
 }

 Here the task to subtract 'A' to every indexing is left to the programmer.

 Maybe the compiler could live with an optional initial index to subtract
 every time
 the array is accessed.


This is a far better idea. What I like in Pascal is the ability to
use 0-based, 1-based or whatever else based arrays depending on
your task and your personal taste. Those who care of speed (me) would
probably use 0-based (and I believe it should be the default, to
work the same way as in C/C++). Otherwise, you can specify it yourself:

    int[5]    foo;     // consists of foo[0] to foo[4]
    int[1..5] bar;     // consists of bar[1] to bar[5]
Feb 22 2002
next sibling parent reply "Walter" <walter digitalmars.com> writes:
"Pavel Minayev" <evilone omen.ru> wrote in message
news:a562qa$5lv$1 digitaldaemon.com...

 This is a far better idea. What I like in Pascal is the ability to
 use 0-based, 1-based or whatever else based arrays depending on
 your task and your personal taste. Those who care of speed (me) would
 probably use 0-based (and I believe it should be the default, to
 work the same way as in C/C++). Otherwise, you can specify it yourself:

     int[5]    foo;     // consists of foo[0] to foo[4]
     int[1..5] bar;     // consists of bar[1] to bar[5]


Having lower bounds specifiable will work with D (and even with C), but in
my decades (!) of programming I've never found a use for it. I came to C
from Basic, FORTRAN, and Pascal. I had some initial trouble getting used to
0 based rather than 1 based, but never looked back. 0 based looked more
'right' to me.
Feb 22 2002
next sibling parent "Roberto Mariottini" <rmariottini lycosmail.com> writes:
"Walter" <walter digitalmars.com> wrote in message
news:a56tc4$1534$2 digitaldaemon.com...

 "Pavel Minayev" <evilone omen.ru> wrote in message
 news:a562qa$5lv$1 digitaldaemon.com...

 This is a far better idea. What I like in Pascal is the ability to
 use 0-based, 1-based or whatever else based arrays depending on
 your task and your personal taste. Those who care of speed (me) would
 probably use 0-based (and I believe it should be the default, to
 work the same way as in C/C++). Otherwise, you can specify it yourself:

     int[5]    foo;     // consists of foo[0] to foo[4]
     int[1..5] bar;     // consists of bar[1] to bar[5]


 Having lower bounds specifiable will work with D (and even with C), but in
 my decades (!) of programming I've never found a use for it. I came to C
 from Basic, FORTRAN, and Pascal.


Instead I have some Pascal sources that will keep as they are. When I do
programming I want to use all features the language provides. And my old
Pascal sources are full of sets, subrange variables, nested procedures,
arbitrary
indexed arrays, and so on.
Automatic code translators simply produce unmaintainable code, once I
started
to translate one of them in C++, but I stopped when I realized I'd have to
work hard
to produce a huge set of classes only to support base Pascal capabilities,
with a
big loss in readability.


 I had some initial trouble getting used to
 0 based rather than 1 based, but never looked back. 0 based looked more
 'right' to me.


Don't confuse normal initial trouble with language expressiveness lack.
I know that, at the end, an array index must be translated to a 0-based
integer.
But simply doing the translation myself doesn't seem to me the right
solution in
most cases.

So I agree with Pavel: array should be 0-based by default, letting the
possibility
to choose a different start index if needed, stating clearly that n-based
indexes are
less performant.

Ciao
Feb 26 2002
prev sibling parent reply "Pavel Minayev" <evilone omen.ru> writes:
"Walter" <walter digitalmars.com> wrote in message
news:a56tc4$1534$2 digitaldaemon.com...


 Having lower bounds specifiable will work with D (and even with C), but in
 my decades (!) of programming I've never found a use for it. I came to C
 from Basic, FORTRAN, and Pascal. I had some initial trouble getting used


to

 0 based rather than 1 based, but never looked back. 0 based looked more
 'right' to me.


Well, there are actually cases where you'd prefer some base other than 0.
As you've seen, many people here consider 1 to be more suitable, and
I understand them... also there are some other cases, for example, suppose
you have an array of year income for 1990-2000, in Pascal you'd probably
declare it as "array[1990 .. 2000] of integer", and then index it like
income[1995], letting the compiler do his job and insert all the necessary
decrements; the result is clean code, easy to read and maintain. In C,
you have to do it all yourself, and probably define some const base = 1990,
and clutter all your code with things like income[1995 - base].

After all, it's as simple as subtracting the base from the index,
a single SUB... ain't it worth the thing?
Feb 27 2002
parent reply "Carlos Santander B." <carlos8294 msn.com> writes:
"Pavel Minayev" <evilone omen.ru> escribió en el mensaje
news:a5jben$16o8$1 digitaldaemon.com...
| "Walter" <walter digitalmars.com> wrote in message
| news:a56tc4$1534$2 digitaldaemon.com...
|
| > Having lower bounds specifiable will work with D (and even with C), but
in
| > my decades (!) of programming I've never found a use for it. I came to C
| > from Basic, FORTRAN, and Pascal. I had some initial trouble getting used
| to
| > 0 based rather than 1 based, but never looked back. 0 based looked more
| > 'right' to me.
|
| Well, there are actually cases where you'd prefer some base other than 0.
| As you've seen, many people here consider 1 to be more suitable, and
| I understand them... also there are some other cases, for example, suppose
| you have an array of year income for 1990-2000, in Pascal you'd probably
| declare it as "array[1990 .. 2000] of integer", and then index it like
| income[1995], letting the compiler do his job and insert all the necessary
| decrements; the result is clean code, easy to read and maintain. In C,
| you have to do it all yourself, and probably define some const base =
1990,
| and clutter all your code with things like income[1995 - base].
|
| After all, it's as simple as subtracting the base from the index,
| a single SUB... ain't it worth the thing?
|
|

No one ever answered to this one. It seems very clever to me.

—————————————————————————
Carlos Santander


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.463 / Virus Database: 262 - Release Date: 2003-03-17
Mar 22 2003
next sibling parent reply Farmer <itsFarmer. freenet.de> writes:
"Carlos Santander B." <carlos8294 msn.com> wrote in
news:b5k815$11ia$2 digitaldaemon.com: 


 "Pavel Minayev" <evilone omen.ru> escribió en el mensaje
 news:a5jben$16o8$1 digitaldaemon.com...
| "Walter" <walter digitalmars.com> wrote in message
| news:a56tc4$1534$2 digitaldaemon.com...
|
| > Having lower bounds specifiable will work with D (and even with C),
| > but 
 in
| > my decades (!) of programming I've never found a use for it. I came
| > to C from Basic, FORTRAN, and Pascal. I had some initial trouble
| > getting used 
| to
| > 0 based rather than 1 based, but never looked back. 0 based looked
| > more 'right' to me.
|
| Well, there are actually cases where you'd prefer some base other
| than 0. As you've seen, many people here consider 1 to be more
| suitable, and I understand them... also there are some other cases,
| for example, suppose you have an array of year income for 1990-2000,
| in Pascal you'd probably declare it as "array[1990 .. 2000] of
| integer", and then index it like income[1995], letting the compiler
| do his job and insert all the necessary decrements; the result is
| clean code, easy to read and maintain. In C, you have to do it all
| yourself, and probably define some const base = 
 1990,
| and clutter all your code with things like income[1995 - base].


Having arrays with base 1 and zero-based index is likely to become a 
maintainer's nightmare: Whenever you see an array, you must look at it's 
declaration (or wait for a tooltip from you IDE) and check whether is zero-
based or not. Array operations become much more bug prone. Once your brain 
adjusted to zero-based indices, you can easily write bug-free code for 
arrays or verify that a given code is bug-free. But switching between 
different bases is very difficult. 

Zero-based indices are favoured over 1-based indices for implementations 
reasons. E.g. with a Byte you can address 256 array elements instead of 
only 255.

In D, there are many ways to express concepts, e.g. functions, classes, D-
structs, templates. I believe that non-zero based arrays are not really 
required to express concepts in away that suitable for the problems, 
programmers have to solve.


Farmer.
Mar 26 2003
next sibling parent "Carlos Santander B." <carlos8294 msn.com> writes:
"Farmer" <itsFarmer. freenet.de> escribió en el mensaje
news:Xns934B78D5F5FDitsFarmer 63.105.9.61...
| "Carlos Santander B." <carlos8294 msn.com> wrote in
| news:b5k815$11ia$2 digitaldaemon.com:
|
| > "Pavel Minayev" <evilone omen.ru> escribió en el mensaje
| > news:a5jben$16o8$1 digitaldaemon.com...
| >| "Walter" <walter digitalmars.com> wrote in message
| >| news:a56tc4$1534$2 digitaldaemon.com...
| >|
| >| > Having lower bounds specifiable will work with D (and even with C),
| >| > but
| > in
| >| > my decades (!) of programming I've never found a use for it. I came
| >| > to C from Basic, FORTRAN, and Pascal. I had some initial trouble
| >| > getting used
| >| to
| >| > 0 based rather than 1 based, but never looked back. 0 based looked
| >| > more 'right' to me.
| >|
| >| Well, there are actually cases where you'd prefer some base other
| >| than 0. As you've seen, many people here consider 1 to be more
| >| suitable, and I understand them... also there are some other cases,
| >| for example, suppose you have an array of year income for 1990-2000,
| >| in Pascal you'd probably declare it as "array[1990 .. 2000] of
| >| integer", and then index it like income[1995], letting the compiler
| >| do his job and insert all the necessary decrements; the result is
| >| clean code, easy to read and maintain. In C, you have to do it all
| >| yourself, and probably define some const base =
| > 1990,
| >| and clutter all your code with things like income[1995 - base].
|
| Having arrays with base 1 and zero-based index is likely to become a
| maintainer's nightmare: Whenever you see an array, you must look at it's
| declaration (or wait for a tooltip from you IDE) and check whether is
zero-
| based or not. Array operations become much more bug prone. Once your brain
| adjusted to zero-based indices, you can easily write bug-free code for
| arrays or verify that a given code is bug-free. But switching between
| different bases is very difficult.
|
| Zero-based indices are favoured over 1-based indices for implementations
| reasons. E.g. with a Byte you can address 256 array elements instead of
| only 255.
|
| In D, there are many ways to express concepts, e.g. functions, classes, D-
| structs, templates. I believe that non-zero based arrays are not really
| required to express concepts in away that suitable for the problems,
| programmers have to solve.
|
|
| Farmer.

I wasn't referring to 1-based arrays only, but any-base arrays. By default,
arrays would be 0-based, but what if we could have:

int [4..14] b; //starts in 4, ends in 13
int [-3..7] c; //starts in -3, ends in 6
int [10] a; //normal array, identical to int[0..10] a

Delphi supports that, and I think it could be an interesting addition.

—————————————————————————
Carlos Santander


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.465 / Virus Database: 263 - Release Date: 2003-03-25
Mar 26 2003
prev sibling next sibling parent reply "Sean L. Palmer" <seanpalmer directvinternet.com> writes:
I disagree.  Nonzero-based arrays buy you convenience.  Now you don't have
to remember to subtract the base, it'll do it automatically.

Not everybody thinks like a pro programmer.  That used to be one of the big
selling points of BASIC that it had 1-based arrays.  I always liked the
feature in Pascal.

If I want to index my array as 2,3,4 for some reason instead of 0,1,2,  why
should the compiler force me to use 0,1,2?  I'll just go and use 2,3,4
anyway but now I have to write a stupid array wrapper class that does the
subtraction for me, or remember to subtract 2 all the time.

I can't think of a good example off the top of my head, but say your indices
are an enum type instead of int.  And let's just say that for instance your
enum type only goes from 8 thru 12 because it also happens to be part of a
hardware register matching some bits you don't have control over.  And you
want to map those hardware states to some other data.  Well you have to
remember to subtract 8 all the time or you'll waste memory or get an array
bounds error.

It's such a simple thing...

D needs a range type.  Then using them for declaring arrays becomes easy;
if it wasn't there you'd wonder why not.

Sean

"Farmer" <itsFarmer. freenet.de> wrote in message
news:Xns934B78D5F5FDitsFarmer 63.105.9.61...

 "Carlos Santander B." <carlos8294 msn.com> wrote in
 news:b5k815$11ia$2 digitaldaemon.com:


 "Pavel Minayev" <evilone omen.ru> escribió en el mensaje
 news:a5jben$16o8$1 digitaldaemon.com...
| "Walter" <walter digitalmars.com> wrote in message
| news:a56tc4$1534$2 digitaldaemon.com...
|
| > Having lower bounds specifiable will work with D (and even with C),
| > but
 in
| > my decades (!) of programming I've never found a use for it. I came
| > to C from Basic, FORTRAN, and Pascal. I had some initial trouble
| > getting used
| to
| > 0 based rather than 1 based, but never looked back. 0 based looked
| > more 'right' to me.
|
| Well, there are actually cases where you'd prefer some base other
| than 0. As you've seen, many people here consider 1 to be more
| suitable, and I understand them... also there are some other cases,
| for example, suppose you have an array of year income for 1990-2000,
| in Pascal you'd probably declare it as "array[1990 .. 2000] of
| integer", and then index it like income[1995], letting the compiler
| do his job and insert all the necessary decrements; the result is
| clean code, easy to read and maintain. In C, you have to do it all
| yourself, and probably define some const base =
 1990,
| and clutter all your code with things like income[1995 - base].


 Having arrays with base 1 and zero-based index is likely to become a
 maintainer's nightmare: Whenever you see an array, you must look at it's
 declaration (or wait for a tooltip from you IDE) and check whether is


zero-

 based or not. Array operations become much more bug prone. Once your brain
 adjusted to zero-based indices, you can easily write bug-free code for
 arrays or verify that a given code is bug-free. But switching between
 different bases is very difficult.

 Zero-based indices are favoured over 1-based indices for implementations
 reasons. E.g. with a Byte you can address 256 array elements instead of
 only 255.

 In D, there are many ways to express concepts, e.g. functions, classes, D-
 structs, templates. I believe that non-zero based arrays are not really
 required to express concepts in away that suitable for the problems,
 programmers have to solve.


 Farmer.
Mar 27 2003
next sibling parent reply Helmut Leitner <helmut.leitner chello.at> writes:
"Sean L. Palmer" wrote:

 
 I disagree.  Nonzero-based arrays buy you convenience.  Now you don't have
 to remember to subtract the base, it'll do it automatically.


Yes, but it will cost any user of an array a little bit of performance
for the potential base correction. If D is seeking to be a successor to
C and C++ in system and game programming, one has to be very careful
with this. 

--
Helmut Leitner    leitner hls.via.at   
Graz, Austria   www.hls-software.com
Mar 27 2003
next sibling parent reply "Sean L. Palmer" <seanpalmer directvinternet.com> writes:
As in C++, you don't pay for what you don't use.  It doesn't necessarily
cost any performance anyway.

If your array is from 1..10, and starts at address 0x80000000, and each
entry is 4 bytes long, the compiler just takes your index and does this to
compute the address:

(index*4)+0x7ffffffc

If it were zero based, it'd do this:

(index*4)+0x80000000

There are situations where it would cost you performance, but not many.

Sean

"Helmut Leitner" <helmut.leitner chello.at> wrote in message
news:3E82FBF5.75FDADF4 chello.at...

 "Sean L. Palmer" wrote:

 I disagree.  Nonzero-based arrays buy you convenience.  Now you don't




have

 to remember to subtract the base, it'll do it automatically.


 Yes, but it will cost any user of an array a little bit of performance
 for the potential base correction. If D is seeking to be a successor to
 C and C++ in system and game programming, one has to be very careful
 with this.
Mar 27 2003
parent reply Helmut Leitner <leitner hls.via.at> writes:
"Sean L. Palmer" wrote:

 There are situations where it would cost you performance, but not many.
 "Helmut Leitner" <helmut.leitner chello.at> wrote in message
 news:3E82FBF5.75FDADF4 chello.at...

 "Sean L. Palmer" wrote:

 I disagree.  Nonzero-based arrays buy you convenience.  Now you don't




 have

 to remember to subtract the base, it'll do it automatically.


 Yes, but it will cost any user of an array a little bit of performance
 for the potential base correction. If D is seeking to be a successor to
 C and C++ in system and game programming, one has to be very careful
 with this.


 
 As in C++, you don't pay for what you don't use.  It doesn't necessarily
 cost any performance anyway.
 
 If your array is from 1..10, and starts at address 0x80000000, and each
 entry is 4 bytes long, the compiler just takes your index and does this to
 compute the address:
 
 (index*4)+0x7ffffffc
 
 If it were zero based, it'd do this:
 
 (index*4)+0x80000000


And when this address in not available at compile time (e. g. an 
element of an dynamically allocate part of an object) or passed
through function call interfaces - how will you do it then without
loss of performance? I think that's impossible.

-- 
Helmut Leitner    leitner hls.via.at
Graz, Austria   www.hls-software.com
Mar 27 2003
next sibling parent "Mike Wynn" <mike.wynn l8night.co.uk> writes:
"Helmut Leitner" <leitner hls.via.at> wrote in message
news:3E833158.D568C839 hls.via.at...

 "Sean L. Palmer" wrote:

 There are situations where it would cost you performance, but not many.
 "Helmut Leitner" <helmut.leitner chello.at> wrote in message
 news:3E82FBF5.75FDADF4 chello.at...

 "Sean L. Palmer" wrote:

 I disagree.  Nonzero-based arrays buy you convenience.  Now you








don't

 have

 to remember to subtract the base, it'll do it automatically.


 Yes, but it will cost any user of an array a little bit of performance
 for the potential base correction. If D is seeking to be a successor






to

 C and C++ in system and game programming, one has to be very careful
 with this.


 As in C++, you don't pay for what you don't use.  It doesn't necessarily
 cost any performance anyway.

 If your array is from 1..10, and starts at address 0x80000000, and each
 entry is 4 bytes long, the compiler just takes your index and does this




to

 compute the address:

 (index*4)+0x7ffffffc

 If it were zero based, it'd do this:

 (index*4)+0x80000000


 And when this address in not available at compile time (e. g. an
 element of an dynamically allocate part of an object) or passed
 through function call interfaces - how will you do it then without
 loss of performance? I think that's impossible.


in C++ any array can be rebased thus;

inline template<T> T * rebase( T * ar, int base ) {
    return &(ar[-base]);
}

or C example
int * myarray = malloc( sizeof(int) * 80 );
....
int * onebase =  &myarray[-1]; // or myarray - 1;

onebase[1] is now myarray[0] :)

in a func call
int func( int * ar ) {
    ar -= 1;  // ar now 1 based.
    .....
}
Mar 27 2003
prev sibling parent reply Mark Evans <Mark_member pathlink.com> writes:
Helmut Leitner says...


And when this address in not available at compile time ...
 - how will you do it then without
loss of performance? I think that's impossible.


That tradeoff the programmer should be allowed to make.  I suspect it's wrong
anyway.  The base value needs computation only once - dynamically or otherwise -
and thereafter may be stored.  Each (random) array access involves at minimum
one addition to find the desired element's memory address.  Using a different
base adds not a whit of extra work.

We had a similar debate about negative indices.  Walter was against them for
performance reasons that are easily addressed if not completely fictitious.
Sean's motto 'pay for what you use' is apropos.

Farmer says...

In D, there are many ways to express concepts, e.g. functions, classes,
D-structs, templates. I believe that non-zero based arrays are not really 
required to express concepts in away that suitable for the problems, 
programmers have to solve.


Functional languages owe much of their fabulous productivity to array (list)
handling capabilities.  An array can hold virtually anything, not just numbers.
It can have more than one dimension to associate objects on different axes en
masse.  C++ folks unfamiliar with such paradigms know little of what they're
missing, so I understand these counteroffers, but there is no substitute.  The
ability to pick apart, rearrange, index, map across, thread, and otherwise sling
arrays around - and morph them into new forms - is a truly expressive and
compact way to write tons of code with performance results comparable to C and
even better, depending on your C programmer and his available time for
optimizing nested inner loops and chasing down off-by-one errors.

Mark
Mar 27 2003
parent Farmer <itsFarmer. freenet.de> writes:
Mark Evans <Mark_member pathlink.com> wrote in
news:b60d0o$2sf7$1 digitaldaemon.com: 


 Farmer says...

In D, there are many ways to express concepts, e.g. functions,
classes, D-structs, templates. I believe that non-zero based arrays
are not really required to express concepts in away that suitable for
the problems, programmers have to solve.


 
 Functional languages owe much of their fabulous productivity to array
 (list) handling capabilities.  An array can hold virtually anything,
 not just numbers. It can have more than one dimension to associate
 objects on different axes en masse.  C++ folks unfamiliar with such
 paradigms know little of what they're missing, so I understand these
 counteroffers, but there is no substitute.  The ability to pick apart,
 rearrange, index, map across, thread, and otherwise sling arrays
 around - and morph them into new forms - is a truly expressive and 
 compact way to write tons of code with performance results comparable
 to C and even better, depending on your C programmer and his available
 time for optimizing nested inner loops and chasing down off-by-one
 errors. 
 
 Mark
 


You are right. I don't know about functional programming, but I know that 

mention C or Pascal).
D arrays really shine when used for system level programming tasks, like 
getting memory from the GC, copying a memory block or working with a rather 
fixed set of objects/values. 
Non-zero based arrays for such tasks have few benefits, but pose the risk 
of harder to maintain code: Some/May people will use different array-bases, 
in the same language, for the same project, for similar concepts.

I think, that D arrays would better stay a low-level, implementation 
determined feature. Putting more features to them, would further increase 
the confusion about them. But (separate) features to the D language and/or 
Phobos, that enables programmers to work with arrays(lists) in a 
productive, safe and reasonably fast manner could be a worthwhile addition 
to D.


Farmer.
Mar 30 2003
prev sibling parent reply Ilya Minkov <midiclub tiscali.de> writes:
Helmut Leitner wrote:

 
 "Sean L. Palmer" wrote:
 

I disagree.  Nonzero-based arrays buy you convenience.  Now you don't have
to remember to subtract the base, it'll do it automatically.


 
 
 Yes, but it will cost any user of an array a little bit of performance
 for the potential base correction. If D is seeking to be a successor to
 C and C++ in system and game programming, one has to be very careful
 with this. 


No, it won't. In Pascal, functions disliked taking arrays of unknown 
size. You could only make them take an array[SomeConstant..] of 
SomeType, then you could process this array as SomeConstant-based. This 
function would only have a run-time specification of an array length, 
but not of a base, and thus wouldn't probably be any slower than a 
0-based array. I'm not sure whether it was allowed to assume that arrays 
had the same base, or type checking had caught such misuse.

-i.
Mar 28 2003
parent reply Helmut Leitner <leitner hls.via.at> writes:
Ilya Minkov wrote:

 
 Helmut Leitner wrote:

 "Sean L. Palmer" wrote:


I disagree.  Nonzero-based arrays buy you convenience.  Now you don't have
to remember to subtract the base, it'll do it automatically.



 Yes, but it will cost any user of an array a little bit of performance
 for the potential base correction. If D is seeking to be a successor to
 C and C++ in system and game programming, one has to be very careful
 with this.


 
 No, it won't. In Pascal, functions disliked taking arrays of unknown
 size. You could only make them take an array[SomeConstant..] of
 SomeType, then you could process this array as SomeConstant-based. This
 function would only have a run-time specification of an array length,
 but not of a base, and thus wouldn't probably be any slower than a
 0-based array. I'm not sure whether it was allowed to assume that arrays
 had the same base, or type checking had caught such misuse.


You are right about Pascal. It was a major PITA that it was impossible
even to write a generic function to e.g . calculate the average of an 
array of arbitrary size because the array size was part of the parameter
type and therefore part of the function definition.

But I don't think that you can compare this. If you want a base != 0,
than you have to pay for it. Maybe not much, but you have to pay.

If you don't offset the array pointer you will have to add the offset
when accessing the array elements.

If you offset the array pointer you need to reset it before you free
it's dynamical memory. So you have to store either the offset or the
pointer to the allocated memory. If you want to implement range
checking, you will have to either use the offset, or store separate
hi and lo bounds. Anyway things become more complicated and it won't
make a single C, C++ or Java programmer feel better about D.

-- 
Helmut Leitner    leitner hls.via.at
Graz, Austria   www.hls-software.com
Mar 28 2003
next sibling parent Ilya Minkov <midiclub 8ung.at> writes:
Helmut Leitner wrote:

 
 Ilya Minkov wrote:

No, it won't. In Pascal, functions disliked taking arrays of unknown
size. You could only make them take an array[SomeConstant..] of
SomeType, then you could process this array as SomeConstant-based. This
function would only have a run-time specification of an array length,
but not of a base, and thus wouldn't probably be any slower than a
0-based array. I'm not sure whether it was allowed to assume that arrays
had the same base, or type checking had caught such misuse.


 
 
 You are right about Pascal. It was a major PITA that it was impossible
 even to write a generic function to e.g . calculate the average of an 
 array of arbitrary size because the array size was part of the parameter
 type and therefore part of the function definition.


It was possible. Only the low bound was fixed, and the length was passed 
implicitly to the function.


 But I don't think that you can compare this. If you want a base != 0,
 than you have to pay for it. Maybe not much, but you have to pay.


Let the base be in the calling code, and let the function accept a 
dynamic array "as if" it was placed on the certain offset. Consider: 
this all offset thingy is good for program readability. And while length 
usually depends on the run-time condition, the base usually depends upon 
readability considerations for algorithms. For example, in a string you 
usually have to iterate from 0 to length-1. That's what all the C guys 
do, they even have a "for" which allows to perfectly hide this fact or 
the oppsite so that a bug is not too easy to see. But isn't it neater to 
reference the string as 1-based?


 If you don't offset the array pointer you will have to add the offset
 when accessing the array elements.


Pointer offset can only be done as a short-term optimisation. Actually, 
i don't even think it's requiered, since almost every memory acess gets 
additive constants in algorithms.

Another example where it is useful, is a syntactic sugar for acessing 
arrays of constant size, like in Sean's example.

You can also make the function programmer handle it: in the upper 
example, he specifies the lower bound, but does not specify the upper 
bound. It is his responsibility to retrieve the upper bound and take it 
into account. The same can be done with a lower bound. The bad thing is 
that it would probably mean expanding the dynamic array specification, 
or would requiere extended function annotation by the compiler.

However, the problem may be of a more general nature, and might be 
better solved in a more generic way, as was pointed out by Mark. I'm not 
sure i exactly understand what specific features/ solution he means though.

-i.
Mar 28 2003
prev sibling parent Mark Evans <Mark_member pathlink.com> writes:
The array record can include both a real base pointer and a pseudo-base pointer
(incorporating the offset). The pseudo-base pointer is computed only once,
whether dynamically or statically.  Array access cost is identical with either
pointer.

Beyond that, the array record could include an 'end' pointer making negative
indexing equally simple.  It would be adjusted every time the length property is
adjusted.

Mark


Helmut Leitner says...

If you want a base != 0,
than you have to pay for it. Maybe not much, but you have to pay.

If you don't offset the array pointer you will have to add the offset
when accessing the array elements.

If you offset the array pointer you need to reset it before you free
it's dynamical memory. So you have to store either the offset or the
pointer to the allocated memory. If you want to implement range
checking, you will have to either use the offset, or store separate
hi and lo bounds. Anyway things become more complicated and it won't
make a single C, C++ or Java programmer feel better about D.

-- 
Helmut Leitner    leitner hls.via.at
Graz, Austria   www.hls-software.com
Mar 28 2003
prev sibling parent Mark Evans <Mark_member pathlink.com> writes:
Base index is nothing next to fundamental array manipulation/creation functions.
Experience stands behind that statement.  Mathematica arrays are 1-based, C
arrays are 0-based, and I must often pass arrays between them.  The 0 vs. 1
issue has never hurt me.

The big deal is that C/C++ offers no help in array manipulation.  That is
primarily why I use Mathematica so regularly.  Mathematica is a multiparadigm
language offering functional-style array manipulations.  I would do these
manipulations in C++ if that were possible.  The more of them in D, the better.

Just to give a flavor of what I mean - here is some Mathematica code pulled at
random.  These lines showcase typical array manipulations and a bit of
functional style.  They come from an autocorrelation spectral estimator that
performs as fast as the equivalent C, but says, in mere lines, what would be
pages of C.

'Table' is equivalent to Sean's 'range' (I think).  'Flatten' drops a
multi-dimensional array down to 1 dimension.    This is the kind of stuff I wish
I could do in D.  -Mark

X = InverseFourier[piece];

auto = Re[Chop[Fourier[X2]]] / Q;
s = Take[auto,M] Table[w[m],{m,1,M}];
s = Flatten[{s,Table[0,{N- (2 M - 1)}]}];
lastpart = Table[auto[[N-m+1 +1]] w[N-m+1],{m,N-M+1+1,N}];
s = Flatten[{s,lastpart}];
capS = Re[Chop[InverseFourier[s]]];



Sean L. Palmer says...

I disagree.  Nonzero-based arrays buy you convenience.  Now you don't have
to remember to subtract the base, it'll do it automatically.
Mar 27 2003
prev sibling parent reply Karl Bochert <kbochert copper.net> writes:
On Wed, 26 Mar 2003 23:45:19 +0000 (UTC), Farmer <itsFarmer. freenet.de> wrote:

 "Carlos Santander B." <carlos8294 msn.com> wrote in
 news:b5k815$11ia$2 digitaldaemon.com: 
 

 "Pavel Minayev" <evilone omen.ru> escribió en el mensaje
 news:a5jben$16o8$1 digitaldaemon.com...
| "Walter" <walter digitalmars.com> wrote in message
| news:a56tc4$1534$2 digitaldaemon.com...
|
| > Having lower bounds specifiable will work with D (and even with C),
| > but 
 in
| > my decades (!) of programming I've never found a use for it. I came
| > to C from Basic, FORTRAN, and Pascal. I had some initial trouble
| > getting used 
| to
| > 0 based rather than 1 based, but never looked back. 0 based looked
| > more 'right' to me.
|
| Well, there are actually cases where you'd prefer some base other
| than 0. As you've seen, many people here consider 1 to be more
| suitable, and I understand them... also there are some other cases,
| for example, suppose you have an array of year income for 1990-2000,
| in Pascal you'd probably declare it as "array[1990 .. 2000] of
| integer", and then index it like income[1995], letting the compiler
| do his job and insert all the necessary decrements; the result is
| clean code, easy to read and maintain. In C, you have to do it all
| yourself, and probably define some const base = 
 1990,
| and clutter all your code with things like income[1995 - base].


 
 Having arrays with base 1 and zero-based index is likely to become a 
 maintainer's nightmare: Whenever you see an array, you must look at it's 
 declaration (or wait for a tooltip from you IDE) and check whether is zero-
 based or not. Array operations become much more bug prone. Once your brain 
 adjusted to zero-based indices, you can easily write bug-free code for 
 arrays or verify that a given code is bug-free. But switching between 
 different bases is very difficult. 
 
 Zero-based indices are favoured over 1-based indices for implementations 
 reasons. E.g. with a Byte you can address 256 array elements instead of 
 only 255.
 
 In D, there are many ways to express concepts, e.g. functions, classes, D-
 structs, templates. I believe that non-zero based arrays are not really 
 required to express concepts in away that suitable for the problems, 
 programmers have to solve.
 
 
 Farmer.


I always get annoyed when people refer to '1-based' arrays. An array whose first
element is arr[1] is a very special beast. Its elements are being labled with
their
position in the array. Access is by ordinal rather than cardinal.

A quick test: Where is the character 's' in the word 'test'?

If you answered "the character offset 2 from the start" then maybe '0-based'
arrays make sense. If you said "the third character" you ought to consider
having arrays accessed by ordinals.

Karl


It is highly misleading to think of '0-based' and '1-based' arrays.  What they
really are
is arrays accessed by index, and arrays accessed by position. An array may have
any arrangment of indices, but it always has a first position. 
I am against 0-based arrays. I am against 1-based arrays. I am for positional
arrays.

Last I looked, D had come up with an absolutely horrible approach to
specifiying slices,
brought on, I'm sure,  by this 'based' concept.
Mar 29 2003
parent reply Mark Evans <Mark_member pathlink.com> writes:
Karl Bochert complains correctly:

If you answered "the character offset 2 from the start" then maybe '0-based'
arrays make sense.


Karl - welcome to the universe of design flaws we call the C programming
language.  Confounding arrays with pointers with strings produces ... C.  Pull
one string, and the whole building collapses.

Disentangling these concepts invites more than one answer to your question.  The
Icon language defines string positions between characters, while general arrays
are "1-based."  Icon is exceptionally adept at string processing.

From the Icon Handbook, "Icon's strings and tables make text processing much
more convenient than in languages that only provide characters and character
arrays....Unlike most languages where strings are implemented as arrays of
characters, Icon provides strings as a primitive data type. They can be of any
length. There are extensive facilities for searching and editing strings."

Unicode with its variable-byte-length encodings makes disentangling strings from
arrays more urgent still.  D should promote strings to primitive type status
with dedicated constructs.  Icon had it right a long time ago.  D is struggling
with Unicode because the confused C model is not amenable to Unicode.  As a
primitive type, Unicode string complexities would vanish under the hood.  I'm
not holding my breath, but if you ask me, that is how to do strings right.
(Those in love with C strings could still declare arrays of char.)

http://www.toolsofcomputing.com/IconHandbook/
http://unicon.sourceforge.net/index.html

Mark
Mar 29 2003
parent reply Antti Sykari <jsykari gamma.hut.fi> writes:
Mark Evans <Mark_member pathlink.com> writes:

 Unicode with its variable-byte-length encodings makes disentangling
 strings from arrays more urgent still.  D should promote strings to
 primitive type status with dedicated constructs.  Icon had it right
 a long time ago.  D is struggling with Unicode because the confused
 C model is not amenable to Unicode.  As a primitive type, Unicode
 string complexities would vanish under the hood.  I'm not holding my
 breath, but if you ask me, that is how to do strings right.  (Those
 in love with C strings could still declare arrays of char.)


One thing D needs for working Unicode strings is a decent foreach (or
iterator) construct, which I suppose is "coming soon". Doing C-like

for (int i = 0; i < string.length; ++i)
  process(string[i]);

is out of the question if the internal representation is, for example,
UTF-8.

Implementing String as a class would not be totally impossible either,
at least if assignment operator could be overloaded.

Of course, the best would probably to have a string concept built into
the language.  As of now, the array type seems to have gathered lot of
the functionality that would in normal circumstances be part of the
string class (how often do you concatenate other arrays than strings,
for example?)


 http://www.toolsofcomputing.com/IconHandbook/
 http://unicon.sourceforge.net/index.html


While Icon is said to be adept at string processing, it's unfortunate
that it doesn't support Unicode either:

---
B3. Is there a Unicode version of Icon?

No. Icon is defined in terms of 8-bit characters, and changing this
presents several design challenges that would likely break existing
programs.
---

-Antti
Mar 29 2003
parent reply Mark Evans <Mark_member pathlink.com> writes:
While Icon is said to be adept at string processing, it's unfortunate
that it doesn't support Unicode either:
-Antti


Icon is recognized worldwide as the king of string processing languages.  Its
development ceased before Unicode came into favor.  Incidentally, if you know of
any language that supports native Unicode strings I am all ears.

One of the Unicon testimonials has it right: "Other languages have minimal data
structures. Most of our programming is in C. Quite often, I need a list of
objects. In C, it is (as you know) a royal pain to declare a structure with a
pointer to itself, and malloc them, free them, and walk the chain. Why can't a
language just have a 'list' datatype, and be done with it? Why can't a language
provide the constructs we all need, instead of providing nearly-assembly-
language constructs and letting us develop the rest ourselves?"

Mark
Mar 29 2003
parent reply "Matthew Wilson" <dmd synesis.com.au> writes:
Depends what you mean by Unicode?


native type.

I'm not aware of any programming language - XML is not a programming
language, all you soap suds! - that works with UTF-8 (or 7). Maybe that's
what you meant?

"Mark Evans" <Mark_member pathlink.com> wrote in message
news:b65see$qsr$1 digitaldaemon.com...

While Icon is said to be adept at string processing, it's unfortunate
that it doesn't support Unicode either:
-Antti


 Icon is recognized worldwide as the king of string processing languages.


Its

 development ceased before Unicode came into favor.  Incidentally, if you


know of

 any language that supports native Unicode strings I am all ears.

 One of the Unicon testimonials has it right: "Other languages have minimal


data

 structures. Most of our programming is in C. Quite often, I need a list of
 objects. In C, it is (as you know) a royal pain to declare a structure


with a

 pointer to itself, and malloc them, free them, and walk the chain. Why


can't a

 language just have a 'list' datatype, and be done with it? Why can't a


language

 provide the constructs we all need, instead of providing nearly-assembly-
 language constructs and letting us develop the rest ourselves?"

 Mark
Mar 29 2003
parent reply Mark Evans <Mark_member pathlink.com> writes:
Matthew Wilson says...




And some languages have seen Unicode retrofits.
http://www.reportlab.com/i18n/python_unicode_tutorial.html
http://rf.net/~james/perli18n.html#Q4

To clarify the remark, I was considering languages that offer Unicode strings as
primitives (not merely characters) and are fast string processors (in the C

Java's String is not a primitive anyway.

Other languages aside, the point is that D needs a Unicode string primitive.

Mark

cter
Mar 29 2003
parent reply "Walter" <walter digitalmars.com> writes:
"Mark Evans" <Mark_member pathlink.com> wrote in message
news:b660it$tn4$1 digitaldaemon.com...

 Other languages aside, the point is that D needs a Unicode string


primitive.

It does already. In D, a char[] is really a utf-8 array.
Mar 31 2003
parent reply Burton Radons <loth users.sourceforge.net> writes:
Walter wrote:

 "Mark Evans" <Mark_member pathlink.com> wrote in message
 news:b660it$tn4$1 digitaldaemon.com...
 

Other languages aside, the point is that D needs a Unicode string


 
 primitive.
 
 It does already. In D, a char[] is really a utf-8 array.


Er, no...

     void main ()
     {
         char[] foo;

         foo = "\uFF00";
     }

"cannot implicitly convert wchar[1] to char[]".  Putting in an explicit 
cast results in a foo with length 1 and value 0.
Mar 31 2003
parent "Walter" <walter digitalmars.com> writes:
Ok, I'll fix it. -Walter

"Burton Radons" <loth users.sourceforge.net> wrote in message
news:b6a7vb$voq$1 digitaldaemon.com...

 Walter wrote:

 "Mark Evans" <Mark_member pathlink.com> wrote in message
 news:b660it$tn4$1 digitaldaemon.com...


Other languages aside, the point is that D needs a Unicode string


 primitive.

 It does already. In D, a char[] is really a utf-8 array.


 Er, no...

      void main ()
      {
          char[] foo;

          foo = "\uFF00";
      }

 "cannot implicitly convert wchar[1] to char[]".  Putting in an explicit
 cast results in a foo with length 1 and value 0.
Mar 31 2003
prev sibling parent Burton Radons <loth users.sourceforge.net> writes:
Carlos Santander B. wrote:

 "Pavel Minayev" <evilone omen.ru> escribió en el mensaje
 news:a5jben$16o8$1 digitaldaemon.com...
 | "Walter" <walter digitalmars.com> wrote in message
 | news:a56tc4$1534$2 digitaldaemon.com...
 |
 | > Having lower bounds specifiable will work with D (and even with C), but
 in
 | > my decades (!) of programming I've never found a use for it. I came to C
 | > from Basic, FORTRAN, and Pascal. I had some initial trouble getting used
 | to
 | > 0 based rather than 1 based, but never looked back. 0 based looked more
 | > 'right' to me.
 |
 | Well, there are actually cases where you'd prefer some base other than 0.
 | As you've seen, many people here consider 1 to be more suitable, and
 | I understand them... also there are some other cases, for example, suppose
 | you have an array of year income for 1990-2000, in Pascal you'd probably
 | declare it as "array[1990 .. 2000] of integer", and then index it like
 | income[1995], letting the compiler do his job and insert all the necessary
 | decrements; the result is clean code, easy to read and maintain. In C,
 | you have to do it all yourself, and probably define some const base =
 1990,
 | and clutter all your code with things like income[1995 - base].
 |
 | After all, it's as simple as subtracting the base from the index,
 | a single SUB... ain't it worth the thing?
 |
 |
 
 No one ever answered to this one. It seems very clever to me.


Putting aside the issue of implementation details, nobody has produced 
any practical examples for it, and I've never seen any good use of it in 
Pascal, either; it's always used static assumptions about the 
environment code is to be used in, as with Pavel's pseudo-example above.
Mar 28 2003
prev sibling next sibling parent "OddesE" <OddesE_XYZ hotmail.com> writes:
"Pavel Minayev" <evilone omen.ru> wrote in message
news:a562qa$5lv$1 digitaldaemon.com...

 "Roberto Mariottini" <rmariottini lycosmail.com> wrote in message
 news:a55s13$1c8a$1 digitaldaemon.com...


<SNIP>

 This is a far better idea. What I like in Pascal is the ability to
 use 0-based, 1-based or whatever else based arrays depending on
 your task and your personal taste. Those who care of speed (me) would
 probably use 0-based (and I believe it should be the default, to
 work the same way as in C/C++). Otherwise, you can specify it yourself:

     int[5]    foo;     // consists of foo[0] to foo[4]
     int[1..5] bar;     // consists of bar[1] to bar[5]



Seconded!


--
Stijn
OddesE_XYZ hotmail.com
http://OddesE.cjb.net
__________________________________________
Remove _XYZ from my address when replying by mail
Feb 27 2002
prev sibling parent reply "OddesE" <OddesE_XYZ hotmail.com> writes:
"Pavel Minayev" <evilone omen.ru> wrote in message
news:a562qa$5lv$1 digitaldaemon.com...

 "Roberto Mariottini" <rmariottini lycosmail.com> wrote in message
 news:a55s13$1c8a$1 digitaldaemon.com...


<SNIP>

 This is a far better idea. What I like in Pascal is the ability to
 use 0-based, 1-based or whatever else based arrays depending on
 your task and your personal taste. Those who care of speed (me) would
 probably use 0-based (and I believe it should be the default, to
 work the same way as in C/C++). Otherwise, you can specify it yourself:

     int[5]    foo;     // consists of foo[0] to foo[4]
     int[1..5] bar;     // consists of bar[1] to bar[5]



And maybe make a property, array.StartIndex so
you could always dynamically find out what the
start index of the array is!


--
Stijn
OddesE_XYZ hotmail.com
http://OddesE.cjb.net
__________________________________________
Remove _XYZ from my address when replying by mail
Feb 27 2002
parent reply "Pavel Minayev" <evilone omen.ru> writes:
"OddesE" <OddesE_XYZ hotmail.com> wrote in message
news:a5jajn$168e$1 digitaldaemon.com...


 And maybe make a property, array.StartIndex so
 you could always dynamically find out what the
 start index of the array is!


Then maybe:

    array.start    // first index
    array.end      // last index
    array.length   // length (end - start + 1)

And define this for all arrays, including 0-based.
Feb 27 2002
parent reply "Sean L. Palmer" <spalmer iname.com> writes:
On a related note, Pascal had succ and pred for enums, but from what I
remember didn't have first and last?

All four would be quite handy to have for enums... unfortunately if you can
define your own values for an enumerant, succ and pred become (at runtime) a
function containing a switch statement or table lookup.

Personally I think enums *should* be sequential, and a separate flags type
could deal with bitflags.  typedef'd ints can handle any other case.

Sean

"Pavel Minayev" <evilone omen.ru> wrote in message
news:a5jb30$16ij$1 digitaldaemon.com...

 "OddesE" <OddesE_XYZ hotmail.com> wrote in message
 news:a5jajn$168e$1 digitaldaemon.com...


 And maybe make a property, array.StartIndex so
 you could always dynamically find out what the
 start index of the array is!


 Then maybe:

     array.start    // first index
     array.end      // last index
     array.length   // length (end - start + 1)

 And define this for all arrays, including 0-based.
Feb 28 2002
parent reply "Pavel Minayev" <evilone omen.ru> writes:
"Sean L. Palmer" <spalmer iname.com> wrote in message
news:a5l3t1$1ua6$1 digitaldaemon.com...


 On a related note, Pascal had succ and pred for enums, but from what I
 remember didn't have first and last?


Yes, right. Succ and Pred, however, were defined for all ordinal
types, not just enums.


 All four would be quite handy to have for enums... unfortunately if you


can

 define your own values for an enumerant, succ and pred become (at runtime)


a

 function containing a switch statement or table lookup.


There's the same problem in Pascal (it supports custom values for
enum members since Delphi 6, AFAIK), and it's handled in a
somewhat strange manner: Succ always means +1, and Pred is -1,
regardless of what declaration says. So:

    type TEnum = (foo = 1000, bar = 2000, baz = 3000);

The thing is, Pascal defines enum as "a subrange whose lowest and
highest values correspond to the lowest and highest ordinalities
of the constants in the declaration". So variable of type TEnum
can take any value in range 1000 .. 3000, and thus, Succ and Pred
just inrements/decrements by one...


 Personally I think enums *should* be sequential, and a separate flags type
 could deal with bitflags.  typedef'd ints can handle any other case.


It is sometimes very convenient to define an enum with members
equal to those of API:

    enum Key
    {
        LButton = 1,
        RButton = 2,
        Cancel = 3,
        MButton = 4,
        Back = 8, BackSpace = Back,
        Tab = 9,
        Clear = 12,
        Return = 13, Enter = Return,
        Shift = 16,
        Control = 17,
        ...
    }

Now every Key, being casted to int, equals the appropriate VK_* constant -
no need for switch() or alike.
Feb 28 2002
parent reply "Sean L. Palmer" <spalmer iname.com> writes:
"Pavel Minayev" <evilone omen.ru> wrote in message
news:a5labi$214t$1 digitaldaemon.com...

 "Sean L. Palmer" <spalmer iname.com> wrote in message
 news:a5l3t1$1ua6$1 digitaldaemon.com...


 On a related note, Pascal had succ and pred for enums, but from what I
 remember didn't have first and last?


 Yes, right. Succ and Pred, however, were defined for all ordinal
 types, not just enums.


Right.  Used it in place of ++ and -- alot.


 All four would be quite handy to have for enums... unfortunately if you


 can

 define your own values for an enumerant, succ and pred become (at




runtime)

 a

 function containing a switch statement or table lookup.


 There's the same problem in Pascal (it supports custom values for
 enum members since Delphi 6, AFAIK), and it's handled in a
 somewhat strange manner: Succ always means +1, and Pred is -1,
 regardless of what declaration says. So:

     type TEnum = (foo = 1000, bar = 2000, baz = 3000);

 The thing is, Pascal defines enum as "a subrange whose lowest and
 highest values correspond to the lowest and highest ordinalities
 of the constants in the declaration". So variable of type TEnum
 can take any value in range 1000 .. 3000, and thus, Succ and Pred
 just inrements/decrements by one...


That's why I think enums should be limited to sequential values.


 Personally I think enums *should* be sequential, and a separate flags




type

 could deal with bitflags.  typedef'd ints can handle any other case.


 It is sometimes very convenient to define an enum with members
 equal to those of API:

     enum Key
     {
         LButton = 1,
         RButton = 2,
         Cancel = 3,
         MButton = 4,
         Back = 8, BackSpace = Back,
         Tab = 9,
         Clear = 12,
         Return = 13, Enter = Return,
         Shift = 16,
         Control = 17,
         ...
     }

 Now every Key, being casted to int, equals the appropriate VK_* constant -
 no need for switch() or alike.


So what's so inconvenient about this?

typedef int VKCode;   // in D I believe this makes a distinct type which
behaves identically to int except for type conversion can't
                                   // be implicitly done from int to VKCode
(though I think the opposite still happens implicitly)
static const VKCode
        LButton = 1,
        RButton = 2,
        Cancel = 3,
        MButton = 4,
        Back = 8, BackSpace = Back,
        Tab = 9,
        Clear = 12,
        Return = 13, Enter = Return,
        Shift = 16,
        Control = 17;  // this is assuming that implicit conversion from int
to VKCode can still be done in the initializer.
                               // if you think about it, that's really an
explicit conversion anyway, don't you think?

That's how I'd like it to be handled, anyway.

Sean
Mar 01 2002
parent reply "Pavel Minayev" <evilone omen.ru> writes:
"Sean L. Palmer" <spalmer iname.com> wrote in message
news:a5nm1p$r0$1 digitaldaemon.com...


 So what's so inconvenient about this?

 typedef int VKCode;   // in D I believe this makes a distinct type which
 behaves identically to int except for type conversion can't
                                    // be implicitly done from int to


VKCode

 (though I think the opposite still happens implicitly)
 static const VKCode
         LButton = 1,
         RButton = 2,
         Cancel = 3,
         MButton = 4,
         Back = 8, BackSpace = Back,
         Tab = 9,
         Clear = 12,
         Return = 13, Enter = Return,
         Shift = 16,
         Control = 17;  // this is assuming that implicit conversion from


int

 to VKCode can still be done in the initializer.
                                // if you think about it, that's really an
 explicit conversion anyway, don't you think?


The difference is that enum defines its own namespace.
So it'd be Key.Enter, Key.Tab, Key.A etc... I don't see
any other way to do it apart from declaring a separate class
specially for that - probably not the best idea...
Mar 01 2002
parent reply "OddesE" <OddesE_XYZ hotmail.com> writes:
"Pavel Minayev" <evilone omen.ru> wrote in message
news:a5nugt$4qh$1 digitaldaemon.com...

 "Sean L. Palmer" <spalmer iname.com> wrote in message
 news:a5nm1p$r0$1 digitaldaemon.com...


 So what's so inconvenient about this?

 typedef int VKCode;   // in D I believe this makes a distinct type which
 behaves identically to int except for type conversion can't
                                    // be implicitly done from int to


 VKCode

 (though I think the opposite still happens implicitly)
 static const VKCode
         LButton = 1,
         RButton = 2,
         Cancel = 3,
         MButton = 4,
         Back = 8, BackSpace = Back,
         Tab = 9,
         Clear = 12,
         Return = 13, Enter = Return,
         Shift = 16,
         Control = 17;  // this is assuming that implicit conversion from


 int

 to VKCode can still be done in the initializer.
                                // if you think about it, that's really




an

 explicit conversion anyway, don't you think?


 The difference is that enum defines its own namespace.
 So it'd be Key.Enter, Key.Tab, Key.A etc... I don't see
 any other way to do it apart from declaring a separate class
 specially for that - probably not the best idea...


How about placing them into it's own module
named Key.d?  Not the most beatiful solution
I agree though...



--
Stijn
OddesE_XYZ hotmail.com
http://OddesE.cjb.net
__________________________________________
Remove _XYZ from my address when replying by mail
Mar 01 2002
parent reply "Pavel Minayev" <evilone omen.ru> writes:
"OddesE" <OddesE_XYZ hotmail.com> wrote in message
news:a5oasr$hqb$1 digitaldaemon.com...


 How about placing them into it's own module
 named Key.d?  Not the most beatiful solution
 I agree though...


Two problems here. First is that there might be another module with
such (frequently used) name. Second is that if another module contains
a function Enter(), you'll have to resolve scope each time you use
it. With enum, you'd always use Key.Enter for key, and Enter() to
call function.
Mar 01 2002
parent "OddesE" <OddesE_XYZ hotmail.com> writes:
"Pavel Minayev" <evilone omen.ru> wrote in message
news:a5omng$lmv$1 digitaldaemon.com...
<SNIP>

 Two problems here. First is that there might be another module with
 such (frequently used) name. Second is that if another module contains
 a function Enter(), you'll have to resolve scope each time you use
 it. With enum, you'd always use Key.Enter for key, and Enter() to
 call function.


Yes you are right, hadn't thought of that.


--
Stijn
OddesE_XYZ hotmail.com
http://OddesE.cjb.net
__________________________________________
Remove _XYZ from my address when replying by mail
Mar 02 2002