• Don Clugston (3/3) Feb 19 2007 Since COW is used so much in D, especially with strings, allowing
• Stewart Gordon (3/6) Feb 20 2007 What would the semantics be exactly?
• Don Clugston (9/15) Feb 20 2007 Just create a new const with the same value as the first one -- all
• Stewart Gordon (8/18) Feb 20 2007 So it would behave as though the programmer typed this rather than
• BCS (3/31) Feb 20 2007 Might the issue be that some function would need the .dup at run time bu...
• Frits van Bommel (6/24) Feb 20 2007 I see no problem with allowing this in compile-time functions. However,
• Don Clugston (7/32) Feb 21 2007 Yes, .dup is useless at compile time. But sometimes you have runtime

Don Clugston <dac nospam.com.au> writes:

Since COW is used so much in D, especially with strings, allowing
"abc".dup to be constant-folded would greatly increase the amount of 
existing code which could be used at compile-time.

Stewart Gordon <smjg_1998 yahoo.com> writes:

Don Clugston Wrote:
 Since COW is used so much in D, especially with strings, allowing 
 "abc".dup to be constant-folded would greatly increase the amount 
 of existing code which could be used at compile-time.

What would the semantics be exactly?

Stewart.

Don Clugston <dac nospam.com.au> writes:

Stewart Gordon wrote:
 Don Clugston Wrote:
 Since COW is used so much in D, especially with strings, allowing 
 "abc".dup to be constant-folded would greatly increase the amount 
 of existing code which could be used at compile-time.

 
 What would the semantics be exactly?

Just create a new const with the same value as the first one -- all 
compile-time consts have value semantics.

ie,
char [] a = "xyz";
char [] b = a.dup;

would be the same as
char [] a = "xyz";
char [] b = "xyz";

Stewart Gordon <smjg_1998 yahoo.com> writes:

Don Clugston Wrote:
<snip>
 Just create a new const with the same value as the first one -- all 
 compile-time consts have value semantics.
 
 ie,
 char [] a = "xyz";
 char [] b = a.dup;
 
 would be the same as
 char [] a = "xyz";
 char [] b = "xyz";

So it would behave as though the programmer typed this rather than

    char[] a = "xyz";
    char[] b = a;

?  There doesn't appear to be any difference.  As I try it (both with and
without const), the two reference the same copy of the string data either way.

But it's probably not defined.  OTOH you could try defining .dup to force the
new constant/variable to reference a new copy; however, there's an ambiguity or
two in this definition.  If you're using .dup to define a struct or class
member initialiser, should it copy only once, or should every instance of the
struct or class contain a new copy?  And what about templates?

Stewart.

BCS <ao pathlink.com> writes:

Reply to Stewart,

 Don Clugston Wrote:
 <snip>
 Just create a new const with the same value as the first one -- all
 compile-time consts have value semantics.
 
 ie,
 char [] a = "xyz";
 char [] b = a.dup;
 would be the same as
 char [] a = "xyz";
 char [] b = "xyz";

 So it would behave as though the programmer typed this rather than
 
 char[] a = "xyz";
 char[] b = a;
 ?  There doesn't appear to be any difference.  As I try it (both with
 and without const), the two reference the same copy of the string data
 either way.
 
 But it's probably not defined.  OTOH you could try defining .dup to
 force the new constant/variable to reference a new copy; however,
 there's an ambiguity or two in this definition.  If you're using .dup
 to define a struct or class member initialiser, should it copy only
 once, or should every instance of the struct or class contain a new
 copy?  And what about templates?
 
 Stewart.
 

Might the issue be that some function would need the .dup at run time but 
can otherwise be used at compile time?

Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:

Don Clugston wrote:
 Stewart Gordon wrote:
 Don Clugston Wrote:
 Since COW is used so much in D, especially with strings, allowing 
 "abc".dup to be constant-folded would greatly increase the amount of 
 existing code which could be used at compile-time.

 What would the semantics be exactly?

 
 Just create a new const with the same value as the first one -- all 
 compile-time consts have value semantics.
 
 ie,
 char [] a = "xyz";
 char [] b = a.dup;
 
 would be the same as
 char [] a = "xyz";
 char [] b = "xyz";

I see no problem with allowing this in compile-time functions. However, 
I can't think of any situation in which this would actually be useful. 
Since compile-time functions aren't allowed to use non-const arrays, 
they aren't allowed to modify elements of any arrays they have access 
to, right? So why would they need .dup?

Don Clugston <dac nospam.com.au> writes:

Frits van Bommel wrote:
 Don Clugston wrote:
 Stewart Gordon wrote:
 Don Clugston Wrote:
 Since COW is used so much in D, especially with strings, allowing 
 "abc".dup to be constant-folded would greatly increase the amount of 
 existing code which could be used at compile-time.

 What would the semantics be exactly?

 Just create a new const with the same value as the first one -- all 
 compile-time consts have value semantics.

 ie,
 char [] a = "xyz";
 char [] b = a.dup;

 would be the same as
 char [] a = "xyz";
 char [] b = "xyz";

 
 I see no problem with allowing this in compile-time functions. However, 
 I can't think of any situation in which this would actually be useful. 
 Since compile-time functions aren't allowed to use non-const arrays, 
 they aren't allowed to modify elements of any arrays they have access 
 to, right? So why would they need .dup?

Yes, .dup is useless at compile time. But sometimes you have runtime 
code that contains things like:

char [] s;
:
return s.dup;

With .dup allowable, that existing code can be used at compile time.