Best way of checking for a templated function instantiation

[Arafel via Digitalmars-d-learn]

Hi,

I'm trying to check at compilation time if a given type 
implements some operator (let's assume it's '+' in this case), 
without caring about the type of the parameters it accepts. Since 
operator overloading is expressed in D through templated 
functions, what is the preferred way of checking if a template is 
/ can be instantiated with a given parameter list?

So far I've come with a solution using __trait(compiles, ...), 
but perhaps it's not 100% reliable -I'm no expert in template 
wizardry-, or there are better options. I also tried with 
hasMember, but it apparantly only shows that "opBinary" is indeed 
present, but nothing more:

---
void main() {
        struct S {
                int opBinary(string op)(int i) if (op == "+") {
                        return 0;
                }
        }

        static assert(__traits(compiles, S.opBinary!"+"));
        static assert(!__traits(compiles, S.opBinary!"-"));
}
---