Instantiating template classes with default template arguments

[Bruno Medeiros]

Sean Kelly wrote:
> Bruno Medeiros wrote:
>> Sean Kelly wrote:
>>>
>>> P.S. In writing this, I discovered that the following code compiles 
>>> when it should not:
>>>
>>>     class C( T = int, U = int ) {}
>>>     class C( T = int, U : char = int ) {}
>>>
>>>     void main()
>>>     {
>>>         auto c = new C!(int);
>>>     }
>>
>> What's wrong with that?
> 
> Oops... you're right.  I edited that from my original example:
> 
>     class C( T = int, U = int ) {}
>     class C( T = int, U : char = char ) {}
> 
>     void main()
>     {
>         auto c = new C!(int);
>     }
> 
> This one shouldn't compile and does.  Unless the defaults are always 
> chosen from the lexically first match?
> 
> 
> 
> Sean

The template that matches is the char one, the second one. It matches 
that one regardless of lexical order. I suspect that's because it is a 
specialization, thus having more priority. For instance, the following 
fails with an ambiguity error:


     class C( T = int, U : int = int ) { pragma(msg,"int");}
     class C( T = int, U : char = char ) { pragma(msg,"char"); }


     void main()
     {
//template instance C!(int) matches more than one template declaration
         auto c = new C!(int);
     }




-- 
Bruno Medeiros - MSc in CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D