How to check for instantiation of specific template?

[simendsjo]

On Thursday, 10 October 2013 at 17:24:37 UTC, H. S. Teoh wrote:
> I have a template used for storing compile-time values:
>
> 	template Def(int x, string y) {
> 		alias impl = TypeTuple!(x,y);
> 	}
>
> How do I define a template isDef that, given some template 
> alias A,
> evaluates to true if A is some instantiation of Def?
>
> 	template isDef(alias A) {
> 		enum A = ... /* what to put here? */
> 	}
>
> The intent is to be able to write signature constraints like 
> this:
>
> 	auto myFunc(alias def)(...)
> 		if (isDef!def)
> 	{
> 		...
> 	}
>
> 	...
> 	// Pass an instantiation of Def to myFunc
> 	auto x = myFunc!(Def!(1, "abc"))(args);
>
> I tried using std.traits.isInstanceOf but apparently it expects 
> the
> second argument to be an actual type, which doesn't work in 
> this case
> because Def is a typetuple of compile-time values, not an 
> actual type.
>
>
> T

I've used this horrible hack to solve this. Not very generic as 
you can see:
     else static if(T.stringof.length > 13 && T.stringof[0..13] == 
"TupleWrapper!")