• bearophile (19/19) Sep 03 2013 Currently this code doesn't work, because the B array is const,
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (11/30) Sep 03 2013 The return type of the lambda is deduced as const(int). I think that is
• H. S. Teoh (7/48) Sep 03 2013 [...]
• bearophile (5/7) Sep 03 2013 Thank you. But the idea of stripping away the const from copied

"bearophile" <bearophileHUGS lycos.com> writes:

Currently this code doesn't work, because the B array is const, 
so B[i] is const:


import std.algorithm: schwartzSort;
void main() {
     auto A = [0, 1, 2];
     const B = [10, -20, 30];
     schwartzSort!(i => B[i])(A);
}


dmd gives:

...\dmd2\src\phobos\std\conv.d(3734): Error: static assert  
"Don't know how to emplace a const(int) with a const(int)."
...\dmd2\src\phobos\std\algorithm.d(9210):        instantiated 
from here: emplace!(const(int), const(int))
test.d(5):        instantiated from here: 
schwartzSort!(__lambda2, "a < b", cast(SwapStrategy)0, int[])


But the array A is mutable. So is it acceptable for me to ask in 
Bugzilla this code to work?

Bye,
bearophile

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 09/03/2013 03:22 PM, bearophile wrote:

 Currently this code doesn't work, because the B array is const, so B[i]
 is const:


 import std.algorithm: schwartzSort;
 void main() {
      auto A = [0, 1, 2];
      const B = [10, -20, 30];
      schwartzSort!(i => B[i])(A);

The return type of the lambda is deduced as const(int). I think that is 
silly. A copied value type should not preserve the const attribute. (I 
vaguely remember discussions on this topic.)

Explicit return type works:

     schwartzSort!(delegate int (i) => B[i])(A);

Playing along with the compiler and casting away const also works:

     schwartzSort!(i => cast()B[i])(A);

 }


 dmd gives:

 ...\dmd2\src\phobos\std\conv.d(3734): Error: static assert "Don't know
 how to emplace a const(int) with a const(int)."
 ...\dmd2\src\phobos\std\algorithm.d(9210):        instantiated from
 here: emplace!(const(int), const(int))
 test.d(5):        instantiated from here: schwartzSort!(__lambda2, "a <
 b", cast(SwapStrategy)0, int[])


 But the array A is mutable. So is it acceptable for me to ask in
 Bugzilla this code to work?

I would think so but I think this issue may already be in bugzilla.

 Bye,
 bearophile

Thanks,
Ali

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Tue, Sep 03, 2013 at 03:57:09PM -0700, Ali Çehreli wrote:
 On 09/03/2013 03:22 PM, bearophile wrote:
 
 Currently this code doesn't work, because the B array is const, so B[i]
 is const:


 import std.algorithm: schwartzSort;
 void main() {
      auto A = [0, 1, 2];
      const B = [10, -20, 30];
      schwartzSort!(i => B[i])(A);

 
 The return type of the lambda is deduced as const(int). I think that
 is silly. A copied value type should not preserve the const
 attribute. (I vaguely remember discussions on this topic.)
 
 Explicit return type works:
 
     schwartzSort!(delegate int (i) => B[i])(A);
 
 Playing along with the compiler and casting away const also works:
 
     schwartzSort!(i => cast()B[i])(A);
 
 }


 dmd gives:

 ...\dmd2\src\phobos\std\conv.d(3734): Error: static assert "Don't know
 how to emplace a const(int) with a const(int)."
 ...\dmd2\src\phobos\std\algorithm.d(9210):        instantiated from
 here: emplace!(const(int), const(int))
 test.d(5):        instantiated from here: schwartzSort!(__lambda2, "a <
 b", cast(SwapStrategy)0, int[])


 But the array A is mutable. So is it acceptable for me to ask in
 Bugzilla this code to work?

 
 I would think so but I think this issue may already be in bugzilla.

[...]

I filed a new issue just in case:

	http://d.puremagic.com/issues/show_bug.cgi?id=10960


T

-- 
"Outlook not so good." That magic 8-ball knows everything! I'll ask about
Exchange Server next. -- (Stolen from the net)

"bearophile" <bearophileHUGS lycos.com> writes:

H. S. Teoh:

 I filed a new issue just in case:

 	http://d.puremagic.com/issues/show_bug.cgi?id=10960

Thank you. But the idea of stripping away the const from copied 
values misses my main point, so I have added a note there.

Bye,
bearophile