How to know if opSlice is defined for a type (including built-in types)?

[chardetm via Digitalmars-d-learn]

Hi everyone,

I was wondering if it was possible to know at compile time if 
opSlice is defined for a type, including built-in types like 
"string". Here is the code I have:


import std.stdio;

struct Test {
	Test opSlice(size_t i, size_t j) {
		return this; // We don't care what it returns
	}
}

void main () {
	string s = "Hello";
	auto s2 = s[0..2];
	static if (is(typeof(&string.opSlice))) writeln("Ok string");
	
	Test t;
	auto t2 = t[0..2];
	static if (is(typeof(&Test.opSlice))) writeln("Ok Test");
}

Output:
Ok Test


How to make it work for "string" too (if possible)? And is there 
a way to differentiate "opSlice()" from "opSlice(size_t, size_t)" 
(or "opSlice(T, T)" for any T)?

Thank you in advance!