Determining if a class has a template function

[Basile B. via Digitalmars-d-learn]

On Tuesday, 11 October 2016 at 20:17:19 UTC, Straivers wrote:
> I have a class T with a templated function foo(string 
> name)(int, int, float) that will be mixed in via template, and 
> I want to determine if that class has mixed it in such that 
> foo(name = "bar"). How could I go about this? Thanks.
>
> eg:
>
> mixin template A(string name, Args...) {
>     void foo(string fooName)(Args args)
>         if (fooName == name) {}
> }
>
> template hasFoo(string name, A) {
>     enum hasFoo = ???
> }
>
> class B {
>     mixin A!("mash", int, int, string);
> }

For this particular example the following solution works:

template A(string name, Args...)
{
     void foo(string fooName)(Args args)
         if (fooName == name) {}
}

template hasFoo(string name, T, V...)
{
     enum hasFoo = __traits(hasMember, T, "foo") &&
         is(typeof(T.foo!name) == typeof(A!(name,V).foo!name));
}

class B
{
     mixin A!("mash", int, int, string);
}

unittest
{
     static assert( hasFoo!("mash", B, int, int , string));
     static assert( !hasFoo!("rash", B, int, uint , string));
}


Now I can't say that I's generic enough to validate any members 
that's injected.
Note well that it wouldn't work with a regular mixin template.

You can also take a look at "std.traits.TemplateOf"