• =?UTF-8?B?Ikx1w61z?= Marques" (24/24) Jun 17 2014 Consider this:
• deadalnix (5/30) Jun 17 2014 No SFINAE please. That is an idiotic C++ idiom. use template
• Dicebot (5/9) Jun 17 2014 As far as I understand Luís wants exactly that, for static assert
• =?UTF-8?B?Ikx1w61z?= Marques" (2/6) Jun 17 2014 Yes, thanks for clarifying.
• deadalnix (2/8) Jun 17 2014 OK I understood it the other way around, sorry. You are right.
• monarch_dodra (11/17) Jun 17 2014 Aren't you just asking for template constraints?
• monarch_dodra (3/4) Jun 17 2014 OK: I re-read the thread. Twice. Now I understand.

=?UTF-8?B?Ikx1w61z?= Marques" <luis luismarques.eu> writes:

Consider this:

     struct S
     {
         void opDispatch(string name, T)(T value)
         {
             alias AllowedTypes = SomeComplexTemplate!S;

             //static assert(is(T : AllowedTypes, "wrong type"));

              static if(!is(T : AllowedTypes))
             {
                 pragma(msg, "wrong type");
                 static assert(0);
             }

         }
     }

If the static assert fails, then the opDispatch instantiation 
fails, and so the relevant member is declared not found. Because 
of SFINAE, I assume (no?), the user/developer will never see the 
"wrong type" error message. So, instead, you have to use a 
pragma(msg), saying something like "hey, ignore the message 
bellow saying 'name' is not found; it's totally there, the 
problem is that you tried to assign a value of an invalid type".

Is there a way to improve this situation?

(BTW, the documentation for opDispatch is a bit thin on the 
details.)

"deadalnix" <deadalnix gmail.com> writes:

On Tuesday, 17 June 2014 at 20:13:39 UTC, Luís Marques wrote:
 Consider this:

     struct S
     {
         void opDispatch(string name, T)(T value)
         {
             alias AllowedTypes = SomeComplexTemplate!S;

             //static assert(is(T : AllowedTypes, "wrong type"));

              static if(!is(T : AllowedTypes))
             {
                 pragma(msg, "wrong type");
                 static assert(0);
             }

         }
     }

 If the static assert fails, then the opDispatch instantiation 
 fails, and so the relevant member is declared not found. 
 Because of SFINAE, I assume (no?), the user/developer will 
 never see the "wrong type" error message. So, instead, you have 
 to use a pragma(msg), saying something like "hey, ignore the 
 message bellow saying 'name' is not found; it's totally there, 
 the problem is that you tried to assign a value of an invalid 
 type".

 Is there a way to improve this situation?

 (BTW, the documentation for opDispatch is a bit thin on the 
 details.)

No SFINAE please. That is an idiotic C++ idiom. use template
constraints if you want to disable this template for some
parameter sets. static assert is to statically assert. In this
case it fails. As it should !

"Dicebot" <public dicebot.lv> writes:

On Tuesday, 17 June 2014 at 20:26:11 UTC, deadalnix wrote:
 No SFINAE please. That is an idiotic C++ idiom. use template
 constraints if you want to disable this template for some
 parameter sets. static assert is to statically assert. In this
 case it fails. As it should !

As far as I understand Luís wants exactly that, for static assert 
to trigger. Looks like some sort of error gagging hides it and 
"parent" error message gets printed instead. D does not support 
SFINAE in general as far as I know.

=?UTF-8?B?Ikx1w61z?= Marques" <luis luismarques.eu> writes:

On Tuesday, 17 June 2014 at 20:41:20 UTC, Dicebot wrote:
 As far as I understand Luís wants exactly that, for static 
 assert to trigger. Looks like some sort of error gagging hides 
 it and "parent" error message gets printed instead. D does not 
 support SFINAE in general as far as I know.

Yes, thanks for clarifying.

"deadalnix" <deadalnix gmail.com> writes:

On Tuesday, 17 June 2014 at 20:54:02 UTC, Luís Marques wrote:
 On Tuesday, 17 June 2014 at 20:41:20 UTC, Dicebot wrote:
 As far as I understand Luís wants exactly that, for static 
 assert to trigger. Looks like some sort of error gagging hides 
 it and "parent" error message gets printed instead. D does not 
 support SFINAE in general as far as I know.

 Yes, thanks for clarifying.

OK I understood it the other way around, sorry. You are right.

"monarch_dodra" <monarchdodra gmail.com> writes:

On Tuesday, 17 June 2014 at 20:54:02 UTC, Luís Marques wrote:
 On Tuesday, 17 June 2014 at 20:41:20 UTC, Dicebot wrote:
 As far as I understand Luís wants exactly that, for static 
 assert to trigger. Looks like some sort of error gagging hides 
 it and "parent" error message gets printed instead. D does not 
 support SFINAE in general as far as I know.

 Yes, thanks for clarifying.

Aren't you just asking for template constraints?

     struct S
     {
         void opDispatch(string name, T)(T value)
         if (T : SomeComplexTemplate!S)
         {
             ...
         }
     }

What am I missing?

"monarch_dodra" <monarchdodra gmail.com> writes:

On Tuesday, 17 June 2014 at 21:45:21 UTC, monarch_dodra wrote:
 What am I missing?

OK: I re-read the thread. Twice. Now I understand.

Looks like a bug.