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digitalmars.D - what was the problem with length prop ?

reply =?ISO-8859-1?Q?Anders_F_Bj=F6rklund?= <afb algonet.se> writes:
Maybe I missed it, but what was the problem
with just using the .length array property ?
Something about templates, or what was it ?

Where was the $ / keyword *needed*, examples ?

--anders
Mar 04 2005
next sibling parent reply "Unknown W. Brackets" <unknown simplemachines.org> writes:
int[] something(int length, int init)
{
	int[] array;

	array.length = length;
	array[0 .. length - 1] = init;

	return array;
}

The "length" parameter is hidden within the array... meaning, on this line:

	array[0 .. length - 1] = init;

The "length" could mean two different things.  It's only within slices 
that it's a problem.

In this example, it's not a problem... but it could easily be one.

-[Unknown]



 Maybe I missed it, but what was the problem
 with just using the .length array property ?
 Something about templates, or what was it ?
 
 Where was the $ / keyword *needed*, examples ?
 
 --anders
Mar 04 2005
parent reply =?ISO-8859-1?Q?Anders_F_Bj=F6rklund?= <afb algonet.se> writes:
Unknown W. Brackets wrote:


 int[] something(int length, int init)
 {
     int[] array;
 
     array.length = length;
     array[0 .. length - 1] = init;
 
     return array;
 }
 
 The "length" parameter is hidden within the array... meaning, on this line:
 
     array[0 .. length - 1] = init;
 
 The "length" could mean two different things.  It's only within slices 
 that it's a problem.


No, not the overloading... What I meant was:

Why wasn't the above code instead written as:

      array.length = length;
      array[0 .. array.length - 1] = init;

Where is the name of the array not known ?
(in what circumstances, I've heard "templates")

--anders
Mar 04 2005
next sibling parent reply "Unknown W. Brackets" <unknown simplemachines.org> writes:
Forgive me; I indeed misunderstood.

It's not, as far as I know.  Just syntactical sugar... but, it is fairly 
nice sugar.  Consider:

Airport.getFromHangar(AIRPLANE_747).optionalComponents["seatbelts"][length 
- 5 .. length]

Okay, strange example, but it's nice to have.  That said, you're right: 
I don't believe there's any specific need for it.

-[Unknown]



 No, not the overloading... What I meant was:
 
 Why wasn't the above code instead written as:
 
      array.length = length;
      array[0 .. array.length - 1] = init;
 
 Where is the name of the array not known ?
 (in what circumstances, I've heard "templates")
 
 --anders
Mar 04 2005
next sibling parent Ben Hinkle <Ben_member pathlink.com> writes:
In article <d0997e$l22$1 digitaldaemon.com>, Unknown W. Brackets says...

Forgive me; I indeed misunderstood.

It's not, as far as I know.  Just syntactical sugar... but, it is fairly 
nice sugar.  Consider:

Airport.getFromHangar(AIRPLANE_747).optionalComponents["seatbelts"][length 
- 5 .. length]

Okay, strange example, but it's nice to have.  That said, you're right: 
I don't believe there's any specific need for it.


Given that C++ and Java have the same issue and neither of those languages have
a special 'length' and I've never heard anyone request one, I don't think this
use case will come up enough to make the special 'length' worth it. But that's
just me...


 No, not the overloading... What I meant was:
 
 Why wasn't the above code instead written as:
 
      array.length = length;
      array[0 .. array.length - 1] = init;
 
 Where is the name of the array not known ?
 (in what circumstances, I've heard "templates")
 
 --anders
Mar 04 2005
prev sibling parent reply =?ISO-8859-1?Q?Anders_F_Bj=F6rklund?= <afb algonet.se> writes:
Unknown W. Brackets wrote:


 It's not, as far as I know.  Just syntactical sugar... but, it is fairly 
 nice sugar.  Consider:
 
 Airport.getFromHangar(AIRPLANE_747).optionalComponents["seatbelts"][length 
 - 5 .. length]
 
 Okay, strange example, but it's nice to have.


So just use a temp ? Too much sugar is not good for you, anyway :-)

--anders
Mar 04 2005
parent Regan Heath <regan netwin.co.nz> writes:
On Fri, 04 Mar 2005 14:01:35 +0100, Anders F Björklund <afb algonet.se> 
wrote:

 Unknown W. Brackets wrote:


 It's not, as far as I know.  Just syntactical sugar... but, it is 
 fairly nice sugar.  Consider:

 Airport.getFromHangar(AIRPLANE_747).optionalComponents["seatbelts"][length 
 - 5 .. length]

 Okay, strange example, but it's nice to have.


 So just use a temp ? Too much sugar is not good for you, anyway :-)


This just occured to me...
(assuming we remove the special length syntactical sugar)

void foo(char[] array) {
   array.length = array.length + 2;
}

...

char[] array;

...

int length = array.length;
if (foo(array) && b = array[0..length]) {}

Basically length becomes invalidated when foo is called, and is incorrect 
(or maybe it's actually correct) in the b = assignment.

Sure, the above example is contrived, it may also be rare, not sure. All I 
know is that it's 'possible'.

Regan
Mar 04 2005
prev sibling parent reply Derek Parnell <derek psych.ward> writes:
On Fri, 04 Mar 2005 10:14:27 +0100, Anders F Björklund wrote:


[snip]



 
 No, not the overloading... What I meant was:
 
 Why wasn't the above code instead written as:
 
       array.length = length;
       array[0 .. array.length - 1] = init;
 
 Where is the name of the array not known ?
 (in what circumstances, I've heard "templates")


It is not *needed*. It just makes reading and writing code easier and less
costly.

Just as 'for', 'foreach', 'switch', 'while', slices, etc... are not needed,
but they sure make code development less troublesome.

-- 
Derek Parnell
Melbourne, Australia
4/03/2005 10:44:05 PM
Mar 04 2005
parent reply =?ISO-8859-1?Q?Anders_F_Bj=F6rklund?= <afb algonet.se> writes:
Derek Parnell wrote:


 It is not *needed*. It just makes reading and writing code easier and less
 costly.


I'm not sure that this whole thread and Kris's problems with
"length" variables qualifies as "less costly", but anyway...


 Just as 'for', 'foreach', 'switch', 'while', slices, etc... are not needed,
 but they sure make code development less troublesome.


Yup, maybe something good can come out of this long debate ?
And that the length var hack somehow can disappear from arrays.

http://www.digitalmars.com/d/changelog.html#new099:

 What's New for D 0.99
 Aug 19, 2004


[...]

 *  Added implicit declaration of length to index and slice expressions.
 This will break existing code if length is used as a variable within [ ]. 


Until then, array.length sounds like the safe bet.
(still waiting for the reason it was introduced ?)

--anders
Mar 04 2005
parent reply Manfred Nowak <svv1999 hotmail.com> writes:
Anders F Björklund <afb algonet.se> wrote:

[...]

 (still waiting for the reason it was introduced ?)


The start of the discussion on the reason seems to be here:
http://www.digitalmars.com/drn-bin/wwwnews?D/24082

And I still think, that this property of arrays is as much needed by 
us, as bicycles are needed by fish.

-manfred
Mar 04 2005
next sibling parent =?ISO-8859-1?Q?Anders_F_Bj=F6rklund?= <afb algonet.se> writes:
Manfred Nowak wrote:


(still waiting for the reason it was introduced ?)


 
 The start of the discussion on the reason seems to be here:
 http://www.digitalmars.com/drn-bin/wwwnews?D/24082


Ah, the good ole negative string indexes...
Just like momma Perl used to make them. :-)

 a = (0..9);  b =  a[0,1,-2,-1]; print  b;
Prints: 0189

--anders
Mar 04 2005
prev sibling parent reply Derek Parnell <derek psych.ward> writes:
On Fri, 4 Mar 2005 19:36:01 +0000 (UTC), Manfred Nowak wrote:


 Anders F Björklund <afb algonet.se> wrote:
 
 [...]

 (still waiting for the reason it was introduced ?)


 
 The start of the discussion on the reason seems to be here:
 http://www.digitalmars.com/drn-bin/wwwnews?D/24082
 
 And I still think, that this property of arrays is as much needed by 
 us, as bicycles are needed by fish.


Are you referring to the ability to reference elements relative to the end
of an array? It is not needed in the same sense that we don't need 'for',
'foreach', 'while', 'switch', etc ... There are other ways of achieving the
same thing, but at the cost of more obscure code and potentially more bugs.

-- 
Derek Parnell
Melbourne, Australia
5/03/2005 8:55:38 AM
Mar 04 2005
parent reply Manfred Nowak <svv1999 hotmail.com> writes:
Derek Parnell <derek psych.ward> wrote:

[...]

 Are you referring to the ability to reference elements relative
 to the end of an array?


No. This needed ability was and is given by the `.length'-property
of arrays. I am referring to the shortcut of this property,
denoted by the quasi-keyword `length' --- or whatever it will be
in the future. 


 It is not needed in the same sense that
 we don't need 'for', 'foreach', 'while', 'switch', etc ... There
 are other ways of achieving the same thing, but at the cost of
 more obscure code and potentially more bugs.


I did not follow that discussion to the end. However, if costs 
where introduced as an argument
1) how have they been defined?
2) why where the cases that led to this new outbreak of the 
discussion not included?
3) please show, that under that cost measure there is no problem 
size, i.e. a natural number "n", for which the relative saving of 
costs becomes neglectable. Where for example "n" is defined to be 
the dimension of a "n"-dimensional cuboid array, which has to be 
reduced into the maximal "n"-dimensional cubed array, that fits 
into the original cuboid array.
4) if you cannot prove number 3), please admit, that your statement 
is wrong, that those well known and accepted elements of blöck-
structured programming, `while' etc., are comparable to the 
shortcut, which is in question here.

-manfed
Mar 04 2005
parent Derek Parnell <derek psych.ward> writes:
On Sat, 5 Mar 2005 01:37:09 +0000 (UTC), Manfred Nowak wrote:


 Derek Parnell <derek psych.ward> wrote:
 
 [...]

 Are you referring to the ability to reference elements relative
 to the end of an array?


 
 No. This needed ability was and is given by the `.length'-property
 of arrays. I am referring to the shortcut of this property,
 denoted by the quasi-keyword `length' --- or whatever it will be
 in the future. 
 

 It is not needed in the same sense that
 we don't need 'for', 'foreach', 'while', 'switch', etc ... There
 are other ways of achieving the same thing, but at the cost of
 more obscure code and potentially more bugs.


 
 I did not follow that discussion to the end. However, if costs 
 where introduced as an argument
 1) how have they been defined?


They (that is "costs where[sic] introduced as an argument") were not
introduced as an argument, therefore the costs were not defined.


 2) why where the cases that led to this new outbreak of the 
 discussion not included?


Just bad luck, I guess. Maybe I'm too lazy. Maybe I'm too arrogant? Maybe I
ran out of time 'cos I had to go shopping with my wife to get our weekly
groceries, two new shirts, a BNC-RCA adaptor for an old VCR I'm trying to
hook up to the new digital TV, a birthday gift for my daughter, ... in
short I've got a life.


 3) please show, that under that cost measure there is no problem 
 size, i.e. a natural number "n", for which the relative saving of 
 costs becomes neglectable. Where for example "n" is defined to be 
 the dimension of a "n"-dimensional cuboid array, which has to be 
 reduced into the maximal "n"-dimensional cubed array, that fits 
 into the original cuboid array.


Sure! 42  ;-)


 4) if you cannot prove number 3), please admit, that your statement 
 is wrong, that those well known and accepted elements of blöck-
 structured programming, `while' etc., are comparable to the 
 shortcut, which is in question here.


I cannot prove (3). Mainly because I can't understand (3). And I do not
admit that my statement was wrong. BTW, what was my statement? 

Was it "There are other ways of achieving the same thing, but at the cost
of more obscure code and potentially more bugs."? This was made in the
context of the 'for' etc line. These would otherwise be implemented with
GOTO statements mainly and I think the literature is generally of the
opinion that GOTO is a cause of more costly software.

In the same manner, I, me, myself, personally, moi, is of the opinion that
a small token of one or two characters, that represents a reference to the
end of an array, is easier to write, read and absorb, than longer ways to
do the same thing. 

I'll try to say it clearly this time ...

A symbolic reference to the end of an array by a *short* token is better
for software developers than a *longer* token.

The only 'proof' I have is personal experience. I'm embarrassed that you
find that lacking in credibility.


 -manfed


WTFWT? 

-- 
Derek Parnell
Melbourne, Australia
5/03/2005 8:49:51 PM
Mar 05 2005
prev sibling parent reply "Regan Heath" <regan netwin.co.nz> writes:
On Fri, 04 Mar 2005 09:47:52 +0100, Anders F Björklund <afb algonet.se>  
wrote:

 Maybe I missed it, but what was the problem
 with just using the .length array property ?
 Something about templates, or what was it ?

 Where was the $ / keyword *needed*, examples ?


[foo.d]
int length = 5;

void main()
{
   int length = 6;
   char[] s;

   s.length = 7;
   s[0..length-1]; // what is the value of the end index?
}

Regan
Mar 04 2005
parent reply David Medlock <amedlock nospam.org> writes:
Regan Heath wrote:

 On Fri, 04 Mar 2005 09:47:52 +0100, Anders F Björklund <afb algonet.se>  
 wrote:
 

 Maybe I missed it, but what was the problem
 with just using the .length array property ?
 Something about templates, or what was it ?

 Where was the $ / keyword *needed*, examples ?


 
 
 [foo.d]
 int length = 5;
 
 void main()
 {
   int length = 6;
   char[] s;
 
   s.length = 7;
   s[0..length-1]; // what is the value of the end index?
 }
 
 Regan



Its too bad the with statement doesnt work with arrays:

int []a = new int[100];
int []x;

with(a) x[0..length] = a[0..length];


Looks pretty clean to me.
Mar 04 2005
parent reply David L. Davis <SpottedTiger yahoo.com> writes:
In article <d09mi9$12o0$1 digitaldaemon.com>, David Medlock says...

Its too bad the with statement doesnt work with arrays:

int []a = new int[100];
int []x;

with(a) x[0..length] = a[0..length];


Looks pretty clean to me.


This looks like a pretty good idea to me!! :) It is clean.

In fact, up until about a couple of months ago I didn't even know that a[ 0 ..
length ] (using length in the array brackets was the same as array.length) was
even allowed, so I've always just coded a[ 0 .. a.length ] instead. (Guess my
code is pretty safe this area, whether "length" ends up being disallowed, or if
we're going to use the "$" as its replacement). But I do feel we should save the
"$" symbol / character tho, for something much more important down the road for
use in D's future development. I'm not sure at this point what that might be,
but I'm very sure something will need it. :)

David L.

-------------------------------------------------------------------
"Dare to reach for the Stars...Dare to Dream, Build, and Achieve!"
Mar 04 2005
parent David Medlock <amedlock nospam.org> writes:
David L. Davis wrote:

 In article <d09mi9$12o0$1 digitaldaemon.com>, David Medlock says...
 

Its too bad the with statement doesnt work with arrays:

int []a = new int[100];
int []x;

with(a) x[0..length] = a[0..length];


Looks pretty clean to me.


 
 
 This looks like a pretty good idea to me!! :) It is clean.
 
 In fact, up until about a couple of months ago I didn't even know that a[ 0 ..
 length ] (using length in the array brackets was the same as array.length) was
 even allowed, so I've always just coded a[ 0 .. a.length ] instead. (Guess my
 code is pretty safe this area, whether "length" ends up being disallowed, or if
 we're going to use the "$" as its replacement). But I do feel we should save
the
 "$" symbol / character tho, for something much more important down the road for
 use in D's future development. I'm not sure at this point what that might be,
 but I'm very sure something will need it. :)
 
 David L.
 
 -------------------------------------------------------------------
 "Dare to reach for the Stars...Dare to Dream, Build, and Achieve!"


With the regex discussion and now using adding a '$' character, I think 
the Perl people have infiltrated this newsgroup...
Mar 04 2005