default args for templates

[monarch_dodra]

On Friday, 17 January 2014 at 12:18:51 UTC, Manu wrote:
> Observing strange behaviour, just want to know if it's 
> correct...
>
> struct VertexBuffer(VertexDataType = void) {}
>
> VertexBuffer x;
>   Error: struct VertexBuffer(VertexDataType = void) is used as 
> a type
>
> auto y = VertexBuffer();
>   Error: struct VertexBuffer(VertexDataType = void) cannot 
> deduce template
> function from argument types !()()
>
> But this works:
> VertexBuffer!() z;
>
>
> Why should I need to supply an empty argument list? This 
> defeats the
> purpose of the default arg, and obscures my code in the common 
> case.
>
> Untyped vertex buffers are the default, and it would be nice to 
> be able to
> declare them trivially.
>
> Also, those error messages are quite unhelpful.

The funny part though is that it works if the template is a 
function.

//----
template foo(T = int)
{
     T foo();
}

void main()
{
     foo(); //Calls foo!int.foo();
}
//----

I guess it's the "()" that saves our butts. Without it, we need 
explicit instantiation:

//----
template foo(T = int)
{
     T foo();
}

void main()
{
     pragma(msg, typeof(foo).stringof);
     pragma(msg, typeof(foo!int).stringof);
}
//----
void
int()
//----