get parameters of a function

[Alex via Digitalmars-d-learn]

On Saturday, 29 April 2017 at 05:58:35 UTC, Stanislav Blinov 
wrote:
> On Friday, 28 April 2017 at 20:43:50 UTC, Alex wrote:
>
> void main()
> {
>     foreach(o1; __traits(getOverloads, S1, "opCall"))
>     {
>         alias P1 = Parameters!o1;
>         foreach(o2; __traits(getOverloads, S2, "opCall"))
>         {
>             alias P2 = Parameters!o2;
>             static if (is(P1 == P2))
>             {
>                 pragma(msg, "Matching params: "~P1.stringof);
>             }
>         }
>     }
> }

The problem is another one: say I have something like this:

import std.traits;

struct A(alias T) if(isCallable!T)
{	
	auto opCall(U...)(U args) if(is(Parameters!T == U)) 
//if(__traits(compiles, T(args)))
	{
		return T(args);
	}
}

void main()
{
	S s;
	A!s c;
	assert(c(4) == 42);
}

struct S
{
	auto opCall(){ return 42; }
	auto opCall(int i){return 42; }
}

This doesn't work because of Parameters trait and the both 
opCalls defined.
However, I see the point...
If I take the compiles-trait, it works as expected:
In this case the constrained is fulfilled, and with the second 
opCall commented out - it isn't.

Thanks :)