• Atila Neves (19/19) Jul 18 2013 http://stackoverflow.com/questions/17724479/in-d-how-do-i-specify-a-vari...
• Andrej Mitrovic (27/32) Jul 18 2013 Here you go:
• Atila Neves (8/41) Jul 18 2013 Thanks! I had to change allSatistfy!(isSomeString, Symbols) to

"Atila Neves" <atila.neves gmail.com> writes:

http://stackoverflow.com/questions/17724479/in-d-how-do-i-specify-a-variadic-template-constraint-on-all-the-whole-tuple

Posted on stackoverflow first since I think it's better for the 
language to get traction there. For completeness sake, posting 
the text of the question here as well:



I'm writing 2 overloads of a function, both of them with variadic 
template compile-time parameters. One should take symbols as the 
templates, the other strings. I want to constrain the template 
instantiation to these two cases. The best I came up with was 
this:

bool func(SYMBOLS...)() if(!is(typeof(SYMBOLS[0]) == string)) {
}

and

bool func(STRINGS...)() if(is(typeof(STRINGS[0]) == string)) {
}

Obviously this only checks the first template parameter, and 
while it works given the code I've written so far, I wish I could 
say "only for all strings" and "only for not all strings". Is 
there a way?

Thanks in advance.

"Andrej Mitrovic" <andrej.mitrovich gmail.com> writes:

On Thursday, 18 July 2013 at 13:18:29 UTC, Atila Neves wrote:
 bool func(SYMBOLS...)() if(!is(typeof(SYMBOLS[0]) == string)) {
 }
 and

 bool func(STRINGS...)() if(is(typeof(STRINGS[0]) == string)) {
 }

Here you go:

-----
import std.string;
import std.traits;
import std.typetuple;
import std.functional;

bool func(Symbols...)(Symbols symbols)
     if (!anySatisfy!(isSomeString, Symbols))
{
     return true;
}

bool func(Strings...)(Strings strings)
     if (allSatisfy!(isSomeString, Strings))
{
     return true;
}

void main()
{
     func("1", "2");
     func(1, 2);
     static assert(!__traits(compiles, func(1, "2")));
}
-----

And remember you have to actually list the runtime arguments 
after the type arguments (e.g. 'Strings strings'), otherwise the 
template won't match.

"Atila Neves" <atila.neves gmail.com> writes:

Thanks! I had to change allSatistfy!(isSomeString, Symbols) to 
allSatistfy!(isSomeString, typeof(Symbols)) but it works.

I don't use the same types as runtimne arguments actually. You 
might see why if/when I finish this particular project and 
announce it.

Shall I answer my own question on stackoverflow?

Atila

On Thursday, 18 July 2013 at 13:25:55 UTC, Andrej Mitrovic wrote:
 On Thursday, 18 July 2013 at 13:18:29 UTC, Atila Neves wrote:
 bool func(SYMBOLS...)() if(!is(typeof(SYMBOLS[0]) == string)) {
 }
 and

 bool func(STRINGS...)() if(is(typeof(STRINGS[0]) == string)) {
 }

 Here you go:

 -----
 import std.string;
 import std.traits;
 import std.typetuple;
 import std.functional;

 bool func(Symbols...)(Symbols symbols)
     if (!anySatisfy!(isSomeString, Symbols))
 {
     return true;
 }

 bool func(Strings...)(Strings strings)
     if (allSatisfy!(isSomeString, Strings))
 {
     return true;
 }

 void main()
 {
     func("1", "2");
     func(1, 2);
     static assert(!__traits(compiles, func(1, "2")));
 }
 -----

 And remember you have to actually list the runtime arguments 
 after the type arguments (e.g. 'Strings strings'), otherwise 
 the template won't match.