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digitalmars.D - The empty statement ";" - when is it useful?

reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
D has ";" as the empty statement. In fact I think it's an empty 
declaration because it can appear at top level.

When is it any good? The only place I can think of is after a label

blah: ;

But then you can always say

blah: {}

which is arguably less puzzling. Any other places?


Andrei
Jul 25 2009
next sibling parent reply Don <nospam nospam.com> writes:
Andrei Alexandrescu wrote:

 D has ";" as the empty statement. In fact I think it's an empty 
 declaration because it can appear at top level.
 
 When is it any good? The only place I can think of is after a label
 
 blah: ;
 
 But then you can always say
 
 blah: {}


Except in an asm block. Can't think of anything else.


 
 which is arguably less puzzling. Any other places?
 
 
 Andrei
Jul 25 2009
parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Don wrote:

 Andrei Alexandrescu wrote:


<snip>

 blah: {}


 
 Except in an asm block. Can't think of anything else.


<snip>

But an asm block doesn't contain D statements, so that's another matter.

Stewart.
Jul 26 2009
parent Don <nospam nospam.com> writes:
Stewart Gordon wrote:

 Don wrote:

 Andrei Alexandrescu wrote:


 <snip>

 blah: {}


 Except in an asm block. Can't think of anything else.


 <snip>
 
 But an asm block doesn't contain D statements, so that's another matter.
 
 Stewart.


Yes, you're right, it's asm syntax -- though it's an asm syntax which 
only exists in D, is copied from the D syntax, and which is actually odd 
and a bit annoying.
(It's particularly annoying in the case where the next line is a version 
statement).
Jul 28 2009
prev sibling next sibling parent reply KennyTM~ <kennytm gmail.com> writes:
Andrei Alexandrescu wrote:

 D has ";" as the empty statement. In fact I think it's an empty 
 declaration because it can appear at top level.
 
 When is it any good? The only place I can think of is after a label
 
 blah: ;
 
 But then you can always say
 
 blah: {}
 
 which is arguably less puzzling. Any other places?
 
 
 Andrei



for (; cond; inc) { ... }


or as the result of a string mixin?
Jul 25 2009
next sibling parent reply BCS <none anon.com> writes:
Hello KennyTM~,


 Andrei Alexandrescu wrote:
 

 D has ";" as the empty statement. In fact I think it's an empty
 declaration because it can appear at top level.
 
 When is it any good? The only place I can think of is after a label
 
 blah: ;
 
 But then you can always say
 
 blah: {}
 
 which is arguably less puzzling. Any other places?
 
 Andrei
 


 for (; cond; inc) { ... }


for({} false; 42) {}


 
 or as the result of a string mixin?
Jul 25 2009
parent Robert Fraser <fraserofthenight gmail.com> writes:
BCS wrote:

 for({} false; 42) {}


Eww...
Jul 26 2009
prev sibling next sibling parent Patrick Kreft <patrick_kreft gmx.net> writes:
KennyTM~ Wrote:


 for (; cond; inc) { ... }


for ( init ; cond; inc ) ...

init and inc are in the most programming language deducible to empty, but the
resulting ';' isnt a empty statement 

so this us legal code:

void main(string[] args)
{
	for(;false;) {
		}
}
Jul 25 2009
prev sibling next sibling parent Stewart Gordon <smjg_1998 yahoo.com> writes:
KennyTM~ wrote:
<snip>

 for (; cond; inc) { ... }


ForStatement:
     for (Initialize Test; Increment) ScopeStatement

Initialize:
     ;
     NoScopeNonEmptyStatement

a syntactic form in its own right, so irrelevant to the general case of 
; as a statement.

Stewart.
Jul 26 2009
prev sibling parent Tim Matthews <tim.matthews7 gmail.com> writes:
On Sun, 26 Jul 2009 02:30:56 +0800
KennyTM~ <kennytm gmail.com> wrote:



 
 for (; cond; inc) { ... }
 



In c++:

#define ever ;;
for(ever) { ... }
Jul 27 2009
prev sibling next sibling parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Andrei Alexandrescu wrote:

 D has ";" as the empty statement. In fact I think it's an empty 
 declaration because it can appear at top level.


<snip>

That's always been one of my peeves.  At least, ever since I discovered 
that preventing such common C typos as

     if (...);
     {
         ...
     }

isn't implemented by disallowing ";" as a statement altogether, even 
though at the time there was nothing in the spec to _allow_ it.

http://d.puremagic.com/issues/show_bug.cgi?id=327

Walter once claimed that it's useful for automatically generated code. 
Though I'm still not quite sure how.

Stewart.
Jul 26 2009
parent reply Don <nospam nospam.com> writes:
Stewart Gordon wrote:

 Andrei Alexandrescu wrote:

 D has ";" as the empty statement. In fact I think it's an empty 
 declaration because it can appear at top level.


 <snip>
 
 That's always been one of my peeves.  At least, ever since I discovered 
 that preventing such common C typos as
 
     if (...);
     {
         ...
     }
 
 isn't implemented by disallowing ";" as a statement altogether, even 
 though at the time there was nothing in the spec to _allow_ it.
 
 http://d.puremagic.com/issues/show_bug.cgi?id=327
 
 Walter once claimed that it's useful for automatically generated code. 
 Though I'm still not quite sure how.


Yes. He's recently the claimed the same thing about the comma operator, 
but I don't buy that argument. I've never needed to use either of them 
myself. (In the case of comma, sure it works as a sequence point when 
you have: a,b, return a; but it doesn't work for a,b, return b; which is 
50% of the cases. I think it's a fallacious argument). Interestingly 
CommaExpression doesn't seem to be defined anywhere in the D spec.



 
 Stewart.
Jul 28 2009
next sibling parent reply Christian Kamm <kamm-incasoftware removethis.de> writes:
Don wrote:

 Interestingly
 CommaExpression doesn't seem to be defined anywhere in the D spec.


It's under the heading of 'Expression':

http://www.digitalmars.com/d/2.0/expression.html#Expression
Jul 28 2009
parent Don <nospam nospam.com> writes:
Christian Kamm wrote:

 Don wrote:

 Interestingly
 CommaExpression doesn't seem to be defined anywhere in the D spec.


 
 It's under the heading of 'Expression':
 
 http://www.digitalmars.com/d/2.0/expression.html#Expression
 


Ah, right. I thought I'd seen it once. 'CommaExpression' is a dead link.
Jul 28 2009
prev sibling parent reply Bill Baxter <wbaxter gmail.com> writes:
On Tue, Jul 28, 2009 at 12:09 AM, Don<nospam nospam.com> wrote:

 Walter once claimed that it's useful for automatically generated code.
 Though I'm still not quite sure how.


 Yes. He's recently the claimed the same thing about the comma operator, but
 I don't buy that argument. I've never needed to use either of them myself.
 (In the case of comma, sure it works as a sequence point when you have: a,b,
 return a; but it doesn't work for a,b, return b; which is 50% of the cases.
 I think it's a fallacious argument). Interestingly CommaExpression doesn't
 seem to be defined anywhere in the D spec.


You meant to say it doesn't work for a,b, return a;  right?
And I don't think that would be 50% of the cases.  a,b,return b seems
much more common.

But either way the argument is ridiculous.  It doesn't need to be as
basic an operator as a single comma just for the sake of making code
generation easier.

--bb
Jul 28 2009
next sibling parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
Bill Baxter wrote:

 On Tue, Jul 28, 2009 at 12:09 AM, Don<nospam nospam.com> wrote:

 Walter once claimed that it's useful for automatically generated code.
 Though I'm still not quite sure how.


 Yes. He's recently the claimed the same thing about the comma operator, but
 I don't buy that argument. I've never needed to use either of them myself.
 (In the case of comma, sure it works as a sequence point when you have: a,b,
 return a; but it doesn't work for a,b, return b; which is 50% of the cases.
 I think it's a fallacious argument). Interestingly CommaExpression doesn't
 seem to be defined anywhere in the D spec.


 
 You meant to say it doesn't work for a,b, return a;  right?
 And I don't think that would be 50% of the cases.  a,b,return b seems
 much more common.
 
 But either way the argument is ridiculous.  It doesn't need to be as
 basic an operator as a single comma just for the sake of making code
 generation easier.


I agree. Walter also mentioned the code generation argument in a 
conversation with me, fully expecting something like "hell yeah" from 
me, but was disappointed :o). If he were right and the comma operator 
would be a net win for better code generation, it would be a net win for 
better handwritten code. But it's not for either; it is some win, but minor.

Anyway, if I had my way I'd eliminate the empty statement ";". It's just 
uselessly hanging in there. It adds half a page total to TDPL just 
because I must first define it and then explain for all of if, while, 
switch, for, foreach... that they can't control an empty statement. If 
the empty statement didn't exist in the first place, I wouldn't be 
wasting readers' time.

BTW, the use of ";" in foreach is not a problem; that use could be 
easily defined as sheer punctuation.


Andrei
Jul 28 2009
parent reply Daniel Keep <daniel.keep.lists gmail.com> writes:
Andrei Alexandrescu wrote:

 Bill Baxter wrote:

 On Tue, Jul 28, 2009 at 12:09 AM, Don<nospam nospam.com> wrote:

 Walter once claimed that it's useful for automatically generated code.
 Though I'm still not quite sure how.


 Yes. He's recently the claimed the same thing about the comma
 operator, but
 I don't buy that argument. I've never needed to use either of them
 myself.
 (In the case of comma, sure it works as a sequence point when you
 have: a,b,
 return a; but it doesn't work for a,b, return b; which is 50% of the
 cases.
 I think it's a fallacious argument). Interestingly CommaExpression
 doesn't
 seem to be defined anywhere in the D spec.


 You meant to say it doesn't work for a,b, return a;  right?
 And I don't think that would be 50% of the cases.  a,b,return b seems
 much more common.

 But either way the argument is ridiculous.  It doesn't need to be as
 basic an operator as a single comma just for the sake of making code
 generation easier.


 
 I agree. Walter also mentioned the code generation argument in a
 conversation with me, fully expecting something like "hell yeah" from
 me, but was disappointed :o). If he were right and the comma operator
 would be a net win for better code generation, it would be a net win for
 better handwritten code. But it's not for either; it is some win, but
 minor.
 
 Anyway, if I had my way I'd eliminate the empty statement ";". It's just
 uselessly hanging in there. It adds half a page total to TDPL just
 because I must first define it and then explain for all of if, while,
 switch, for, foreach... that they can't control an empty statement. If
 the empty statement didn't exist in the first place, I wouldn't be
 wasting readers' time.
 
 BTW, the use of ";" in foreach is not a problem; that use could be
 easily defined as sheer punctuation.
 
 
 Andrei


U comma(T,U)(T a, U b) { return b; }

Is there any reason you couldn't use something like that?
Jul 28 2009
next sibling parent Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
Daniel Keep wrote:

 Andrei Alexandrescu wrote:

 Bill Baxter wrote:

 On Tue, Jul 28, 2009 at 12:09 AM, Don<nospam nospam.com> wrote:

 Walter once claimed that it's useful for automatically generated code.
 Though I'm still not quite sure how.


 Yes. He's recently the claimed the same thing about the comma
 operator, but
 I don't buy that argument. I've never needed to use either of them
 myself.
 (In the case of comma, sure it works as a sequence point when you
 have: a,b,
 return a; but it doesn't work for a,b, return b; which is 50% of the
 cases.
 I think it's a fallacious argument). Interestingly CommaExpression
 doesn't
 seem to be defined anywhere in the D spec.


 You meant to say it doesn't work for a,b, return a;  right?
 And I don't think that would be 50% of the cases.  a,b,return b seems
 much more common.

 But either way the argument is ridiculous.  It doesn't need to be as
 basic an operator as a single comma just for the sake of making code
 generation easier.


 I agree. Walter also mentioned the code generation argument in a
 conversation with me, fully expecting something like "hell yeah" from
 me, but was disappointed :o). If he were right and the comma operator
 would be a net win for better code generation, it would be a net win for
 better handwritten code. But it's not for either; it is some win, but
 minor.

 Anyway, if I had my way I'd eliminate the empty statement ";". It's just
 uselessly hanging in there. It adds half a page total to TDPL just
 because I must first define it and then explain for all of if, while,
 switch, for, foreach... that they can't control an empty statement. If
 the empty statement didn't exist in the first place, I wouldn't be
 wasting readers' time.

 BTW, the use of ";" in foreach is not a problem; that use could be
 easily defined as sheer punctuation.


 Andrei


 
 U comma(T,U)(T a, U b) { return b; }
 
 Is there any reason you couldn't use something like that?


Absolutely! And now that order of evaluation will be defined to be 
left-to-right in D, the semantics would be quite the same.


Andrei
Jul 28 2009
prev sibling parent reply Arthur Lloyd <via google.com> writes:
Daniel Keep Wrote:


 U comma(T,U)(T a, U b) { return b; }
 
 Is there any reason you couldn't use something like that?


Sorry, this is probably a newbie question, but.. So instead of return a, b, c;
you now have to write return comma(a, comma(b, c)); ? How will that help?
Jul 28 2009
next sibling parent reply Jarrett Billingsley <jarrett.billingsley gmail.com> writes:
 Tue, Jul 28, 2009 at 2:28 PM, Arthur Lloyd<via google.com> wrote:

 Daniel Keep Wrote:


 U comma(T,U)(T a, U b) { return b; }

 Is there any reason you couldn't use something like that?


 Sorry, this is probably a newbie question, but.. So instead of return a, b, c;
you now have to write return comma(a, comma(b, c)); ? How will that help?


typeof(T[$ - 1]) comma(T...)(T args) { return args[$ - 1]; }

There.  Now you can do "comma(a, b, c)".
Jul 28 2009
parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Jarrett Billingsley wrote:

  Tue, Jul 28, 2009 at 2:28 PM, Arthur Lloyd<via google.com> wrote:

 Daniel Keep Wrote:


 U comma(T,U)(T a, U b) { return b; }

 Is there any reason you couldn't use something like that?


 Sorry, this is probably a newbie question, but.. So instead of return a, b, c;
you now have to write return comma(a, comma(b, c)); ? How will that help?


 
 typeof(T[$ - 1]) comma(T...)(T args) { return args[$ - 1]; }
 
 There.  Now you can do "comma(a, b, c)".


Still won't solve the problem Andrei rightly pointed out.  But this will:

T[$-1] comma(T...)(lazy T args) {
     foreach (a; args[0..$-1]) cast(void) a;
     return args[$-1];
}

Stewart.
Jul 28 2009
parent reply Jarrett Billingsley <jarrett.billingsley gmail.com> writes:
On Tue, Jul 28, 2009 at 5:46 PM, Stewart Gordon<smjg_1998 yahoo.com> wrote:

 Jarrett Billingsley wrote:

 =A0Tue, Jul 28, 2009 at 2:28 PM, Arthur Lloyd<via google.com> wrote:

 Daniel Keep Wrote:


 U comma(T,U)(T a, U b) { return b; }

 Is there any reason you couldn't use something like that?


 Sorry, this is probably a newbie question, but.. So instead of return a=






,

 b, c; you now have to write return comma(a, comma(b, c)); ? How will th=






at

 help?


 typeof(T[$ - 1]) comma(T...)(T args) { return args[$ - 1]; }

 There. =A0Now you can do "comma(a, b, c)".


 Still won't solve the problem Andrei rightly pointed out. =A0But this wil=


l:

 T[$-1] comma(T...)(lazy T args) {
 =A0 =A0foreach (a; args[0..$-1]) cast(void) a;
 =A0 =A0return args[$-1];
 }


For one, that's almost verbatim what Tom S suggested in "comma
expressions must die."

For two, what problem did Andrei point out?  Order of evaluation of
function arguments?  On the contrary, he said "now that order of
evaluation will be defined to be left-to-right in D, the semantics
would be quite the same".  Your code is what you'd have to use in D1,
but in D2, the simpler version would suffice.
Jul 28 2009
parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Jarrett Billingsley wrote:
<snip>

 For two, what problem did Andrei point out?  Order of evaluation of
 function arguments?  On the contrary, he said "now that order of
 evaluation will be defined to be left-to-right in D, the semantics
 would be quite the same".  Your code is what you'd have to use in D1,
 but in D2, the simpler version would suffice.


What do you understand by the combination of "now" and "will be"?

I understood that he was speaking either sarcastically or hypothetically.

Or can you find any official statement of this change, let alone a 
rationale for it?

Stewart.
Jul 28 2009
next sibling parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
Stewart Gordon wrote:

 Jarrett Billingsley wrote:
 <snip>

 For two, what problem did Andrei point out?  Order of evaluation of
 function arguments?  On the contrary, he said "now that order of
 evaluation will be defined to be left-to-right in D, the semantics
 would be quite the same".  Your code is what you'd have to use in D1,
 but in D2, the simpler version would suffice.


 
 What do you understand by the combination of "now" and "will be"?
 
 I understood that he was speaking either sarcastically or hypothetically.
 
 Or can you find any official statement of this change, let alone a 
 rationale for it?


No, sorry. Usually I strive to be precise, but this time I just wasn't. 
The plan is to define order of evaluation to be lexical order. Somehow I 
can't convince Walter that that means assignment too!

e1[e2] = e3;

means:

1. Evaluate e1

2. Evaluate e2

3. Evaluate []

4. Evaluate e3

5. Evaluate assignment.

Walter wants:

1. Evaluate e3. Why in the world, I have no idea.

2, 3. Evaluate e1 and e2, I'm not sure in which order he thinks is right

4. Evaluate []

4. Evaluate =

Lexical order rules. Lexical order dammit!

Walter and I see eye to eye probably 95% of the time, which has two 
disadvantages: (a) everybody here thinks one is influencing the other 
when in fact most of the time we arrive at the same conclusion from very 
different paths, (b) the remaining 5% are disconcerting. This is one of 
those cases.


Andrei
Jul 28 2009
parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Andrei Alexandrescu wrote:
<snip>

 No, sorry. Usually I strive to be precise, but this time I just wasn't. 
 The plan is to define order of evaluation to be lexical order. Somehow I 
 can't convince Walter that that means assignment too!


<snip>

I still would like to know where you found that plan!

The decision to leave order of evaluation unspecified was a deliberate 
one at the time, and for good reasons.

One of these reasons was to open the option of evaluating subexpressions 
in parallel.  I'm not sure what the others were, but another 
optimisation potential that comes to my mind is to minimise the working 
memory while still allowing expressions to be written in an intuitive order.

Who has decided that these reasons are no longer good, and why?

Stewart.
Jul 29 2009
parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
Stewart Gordon wrote:

 Andrei Alexandrescu wrote:
 <snip>

 No, sorry. Usually I strive to be precise, but this time I just 
 wasn't. The plan is to define order of evaluation to be lexical order. 
 Somehow I can't convince Walter that that means assignment too!


 <snip>
 
 I still would like to know where you found that plan!
 
 The decision to leave order of evaluation unspecified was a deliberate 
 one at the time, and for good reasons.
 
 One of these reasons was to open the option of evaluating subexpressions 
 in parallel.  I'm not sure what the others were, but another 
 optimisation potential that comes to my mind is to minimise the working 
 memory while still allowing expressions to be written in an intuitive 
 order.
 
 Who has decided that these reasons are no longer good, and why?


This has been a source of long discussion in C++ circles, and Walter and 
I have also discussed the matter several times. Defining order of 
evaluation has good benefits, and the loss in efficiency has with time 
been reduced to just a few corner cases that don't seem to justify the 
cost anymore. Note that operations can still be evaluated in parallel as 
long as there's no dependencies between them.

Andrei
Jul 29 2009
next sibling parent reply BCS <ao pathlink.com> writes:
Reply to Andrei,


 Stewart Gordon wrote:
 

 One of these reasons was to open the option of evaluating
 subexpressions in parallel.  I'm not sure what the others were, but
 another optimisation potential that comes to my mind is to minimise
 the working memory while still allowing expressions to be written in
 an intuitive order.
 
 Who has decided that these reasons are no longer good, and why?
 


 Note that operations can still be evaluated in parallel
 as long as there's no dependencies between them.
 
 Andrei
 


You could go with "apparent order", that is the code can work anyway it wants 
as long as the end effect is the same as if the order was per the spec.
Jul 29 2009
parent Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
BCS wrote:

 Reply to Andrei,
 

 Stewart Gordon wrote:


 One of these reasons was to open the option of evaluating
 subexpressions in parallel.  I'm not sure what the others were, but
 another optimisation potential that comes to my mind is to minimise
 the working memory while still allowing expressions to be written in
 an intuitive order.

 Who has decided that these reasons are no longer good, and why?


 Note that operations can still be evaluated in parallel
 as long as there's no dependencies between them.

 Andrei


 
 You could go with "apparent order", that is the code can work anyway it 
 wants as long as the end effect is the same as if the order was per the 
 spec.


That's the plan.

Andrei
Jul 29 2009
prev sibling parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Andrei Alexandrescu wrote:
<snip>

 This has been a source of long discussion in C++ circles, and Walter and 
 I have also discussed the matter several times. Defining order of 
 evaluation has good benefits, and the loss in efficiency has with time 
 been reduced to just a few corner cases that don't seem to justify the 
 cost anymore. Note that operations can still be evaluated in parallel as 
 long as there's no dependencies between them.


So the compiler would be allowed to parallelise only if it can determine 
that the two subexpressions don't depend on each other?  This could get 
complicated when you consider calculations that are involved enough to 
be worth parallelising in the first place.

Stewart.
Jul 29 2009
parent Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
Stewart Gordon wrote:

 Andrei Alexandrescu wrote:
 <snip>

 This has been a source of long discussion in C++ circles, and Walter 
 and I have also discussed the matter several times. Defining order of 
 evaluation has good benefits, and the loss in efficiency has with time 
 been reduced to just a few corner cases that don't seem to justify the 
 cost anymore. Note that operations can still be evaluated in parallel 
 as long as there's no dependencies between them.


 
 So the compiler would be allowed to parallelise only if it can determine 
 that the two subexpressions don't depend on each other?


Yes.


 This could get 
 complicated when you consider calculations that are involved enough to 
 be worth parallelising in the first place.


Quite the contrary, in fact. Involved calculations in a given expression 
entail more often than not complicated operations as opposed to 
complicated updates.


Andrei
Jul 29 2009
prev sibling parent reply Jarrett Billingsley <jarrett.billingsley gmail.com> writes:
On Tue, Jul 28, 2009 at 7:46 PM, Stewart Gordon<smjg_1998 yahoo.com> wrote:

 Jarrett Billingsley wrote:
 <snip>

 For two, what problem did Andrei point out? =A0Order of evaluation of
 function arguments? =A0On the contrary, he said "now that order of
 evaluation will be defined to be left-to-right in D, the semantics
 would be quite the same". =A0Your code is what you'd have to use in D1,
 but in D2, the simpler version would suffice.


 What do you understand by the combination of "now" and "will be"?

 I understood that he was speaking either sarcastically or hypothetically.

 Or can you find any official statement of this change, let alone a ration=


ale

 for it?

 Stewart.


http://www.digitalmars.com/d/archives/digitalmars/D/assignment_left-to-righ=
t_or_right-to-left_evaluation_89616.html

That's the thread I remember it being discussed on.

Also, this is the second time your reply has broken threading, at
least on the mailing list..
Jul 28 2009
parent Stewart Gordon <smjg_1998 yahoo.com> writes:
Jarrett Billingsley wrote:

 On Tue, Jul 28, 2009 at 7:46 PM, Stewart Gordon<smjg_1998 yahoo.com> wrote:


<snip>

 Or can you find any official statement of this change, let alone a rationale
 for it?


 http://www.digitalmars.com/d/archives/digitalmars/D/assignment_left-to-right_or_right-to-left_evaluation_89616.html
 
 That's the thread I remember it being discussed on.


In which Walter hasn't posted anything ... unless the archiver dropped it.


 Also, this is the second time your reply has broken threading, at
 least on the mailing list..


It hasn't broken threading as I view it in Thunderbird.  It sounds to me 
like a bug in the mailing list.

Is anybody else seeing this thread broken (other than through the web 
interface, where this is a known problem)?

Stewart.
Jul 29 2009
prev sibling parent Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
Arthur Lloyd wrote:

 Daniel Keep Wrote:
 

 U comma(T,U)(T a, U b) { return b; }

 Is there any reason you couldn't use something like that?


 
 Sorry, this is probably a newbie question, but.. So instead of return a, b, c;
you now have to write return comma(a, comma(b, c)); ? How will that help?


I think he just means that the comma operator is not a strategic 
advantage for automated code generation.

Andrei
Jul 28 2009
prev sibling parent Don <nospam nospam.com> writes:
Bill Baxter wrote:

 On Tue, Jul 28, 2009 at 12:09 AM, Don<nospam nospam.com> wrote:

 Walter once claimed that it's useful for automatically generated code.
 Though I'm still not quite sure how.


 Yes. He's recently the claimed the same thing about the comma operator, but
 I don't buy that argument. I've never needed to use either of them myself.
 (In the case of comma, sure it works as a sequence point when you have: a,b,
 return a; but it doesn't work for a,b, return b; which is 50% of the cases.
 I think it's a fallacious argument). Interestingly CommaExpression doesn't
 seem to be defined anywhere in the D spec.


 
 You meant to say it doesn't work for a,b, return a;  right?


Yes.

 And I don't think that would be 50% of the cases.  a,b,return b seems
 much more common.


The only time I've considered using comma is with:   assert(a); b = 
foo(a); assert(c); return b;
But you're probably right, it's less than 50% of the time in practice.


 But either way the argument is ridiculous.  It doesn't need to be as
 basic an operator as a single comma just for the sake of making code
 generation easier.
 
 --bb
Jul 28 2009
prev sibling next sibling parent reply Arthur Lloyd <via google.com> writes:
Andrei Alexandrescu Wrote:


 I think he just means that the comma operator is not a strategic 
 advantage for automated code generation.


If the comma operator does not offer a strategic advantage, will it be
deprecated in favor of something that python and ruby do. I've many times
fallen into a trap when initializing multidim arrays, like:




Also





seems very verbose when in a scripting language I can do:




Does this work, if the comma builds a tuple instead of a sequence?
Jul 29 2009
parent reply "Adam D. Ruppe" <destructionator gmail.com> writes:
On Wed, Jul 29, 2009 at 10:29:51AM -0400, Arthur Lloyd wrote:

 Also
 



 
 seems very verbose when in a scripting language I can do:


It also seems very verbose in D where you can do:

auto getThem() { return tuple(4,5); }
auto a = getThem;

-- 
Adam D. Ruppe
http://arsdnet.net
Jul 29 2009
parent reply Arthur Lloyd <via google.com> writes:
Adam D. Ruppe Wrote:


 On Wed, Jul 29, 2009 at 10:29:51AM -0400, Arthur Lloyd wrote:

 Also
 



 
 seems very verbose when in a scripting language I can do:


 
 It also seems very verbose in D where you can do:
 
 auto getThem() { return tuple(4,5); }
 auto a = getThem;


No, that looks quite good. Is the tuple() a D2 feature? D1/Tango doesn't seem
to have it? Why not even go so far as to make the tuple keyword completely
optional?
Jul 29 2009
parent "Adam D. Ruppe" <destructionator gmail.com> writes:
On Wed, Jul 29, 2009 at 11:00:13AM -0400, Arthur Lloyd wrote:

 No, that looks quite good. Is the tuple() a D2 feature? D1/Tango doesn't seem
to have it? Why not even go so far as to make the tuple keyword completely
optional?


It is part of phobos 2, in std.typecons. (so you'd actually need to stick

import std.typecons;

at the top of the file to get that to compile.)


Since it is a library solution, there is no actual keyword here, nor can
it do the length thing you wanted. But, it does cover the other case quite
well, without needing to change the language at all.


-- 
Adam D. Ruppe
http://arsdnet.net
Jul 29 2009
prev sibling parent Arthur Lloyd <via google.com> writes:
Adam D. Ruppe Wrote:


 On Wed, Jul 29, 2009 at 11:00:13AM -0400, Arthur Lloyd wrote:

 No, that looks quite good. Is the tuple() a D2 feature? D1/Tango doesn't seem
to have it? Why not even go so far as to make the tuple keyword completely
optional?


 
 It is part of phobos 2, in std.typecons. (so you'd actually need to stick
 
 import std.typecons;
 
 at the top of the file to get that to compile.)
 
 
 Since it is a library solution, there is no actual keyword here, nor can
 it do the length thing you wanted. But, it does cover the other case quite
 well, without needing to change the language at all.


Does the language get too complex if this feature "gets in"? I mean you don't
need to write



or



but for some reason tuple(1, 2). On the other hand you need to write 'lambda'
in python when constructing inline functions. The 'lambda' is omitted in D and
'tuple' in Python. So a mixture of these languages could omit both!
Jul 29 2009