Why the compiler chooses the template with tuple paramer? Isn't the template with type parameter more 'specialized'?

template Foo(T)
{
	pragma(msg, "Type");
}

template Foo(TT...)
{
	pragma(msg, "Tuple");
}

alias Foo!(int) foo;
----
Outputs: Tuple

Max Samukha wrote:
> Why the compiler chooses the template with tuple paramer? Isn't the
> template with type parameter more 'specialized'?
> 
> template Foo(T)
> {
> 	pragma(msg, "Type");
> }
> 
> template Foo(TT...)
> {
> 	pragma(msg, "Tuple");
> }
> 
> alias Foo!(int) foo;
> ----
> Outputs: Tuple

I don't think the spec makes any promises about that sort of thing. Generally speaking you're on shaky ground any time you try to overload templates in D.

Can you not put a "static if(TT.length==1)" in the tuple version?

Also you could try making the tuple one be

    template Foo(T0,T1,TN...) {
          alias Tuple!(T0,T1,TN) TT;
    }

So that it takes a min of 2 args to differentiate.  And then add a zero arg version if you need that too.

But I think Walter's idea with templates is that to make it simpler any ambiguity should just be an error.  So that you don't end up with a bunch of crazy rules that no two compilers implement quite the same.

--bb

On Tue, 22 Apr 2008 20:05:21 +0900, Bill Baxter <dnewsgroup@billbaxter.com> wrote:

>Max Samukha wrote:
>> Why the compiler chooses the template with tuple paramer? Isn't the template with type parameter more 'specialized'?
>> 
>> template Foo(T)
>> {
>> 	pragma(msg, "Type");
>> }
>> 
>> template Foo(TT...)
>> {
>> 	pragma(msg, "Tuple");
>> }
>> 
>> alias Foo!(int) foo;
>> ----
>> Outputs: Tuple
>
>I don't think the spec makes any promises about that sort of thing. Generally speaking you're on shaky ground any time you try to overload templates in D.
>
>Can you not put a "static if(TT.length==1)" in the tuple version?
>
>Also you could try making the tuple one be
>
>     template Foo(T0,T1,TN...) {
>           alias Tuple!(T0,T1,TN) TT;
>     }
>
>So that it takes a min of 2 args to differentiate.  And then add a zero arg version if you need that too.

Yeah, I did something similar.
>
>But I think Walter's idea with templates is that to make it simpler any ambiguity should just be an error.  So that you don't end up with a bunch of crazy rules that no two compilers implement quite the same.
>
>--bb

Agree that this should probably result in an error. There is also an inconsistency in the current implementation (dmd 2.012, http://d.puremagic.com/issues/show_bug.cgi?id=2025).