is expression for template structs/classes instances?

[Jonathan M Davis]

On Tuesday, December 21, 2010 02:57:45 d coder wrote:
> > I do know the template. I will try out your solution. Will let you
> > know if I face issues.
> 
> Simen
> 
> It works perfect, And this is exactly what I was looking for. If you
> see my original post, I also thought this form of "is" expression
> should work. Just could not get around to the right syntax.
> 
> With your help it is working now. I am using a slightly more elaborate
> check which is obvious but I am writing it here to just let the list
> know.
> 
> static if ( is( typeof(foo) f == S!T, T : int) ) {
>   // foo is an object of type S!T
>   // where T is convertible to int
> }

Yes, that sort of thing works. The problem is when you want to know whether an 
arbitrary type is an instantiation of a particular template. For instance, if 
you have

struct S(T)
{
}

struct Q(T)
{
}

and you pass S!int to Q - Q(S!int) - Q sees S!int is a specific type, not an 
instantiation of S, so it's difficult to have a template constraint checking that 
the type passed to Q is an instantiation of S. However, if you know exactly 
which instantiation that you're checking for, then it's relatively easy.

- Jonathan M Davis