Operator overloading

[Xan]

Hi, I read http://dlang.org/operatoroverloading.html but in my 
code it does not work. I tried to overload '*' binary operator in 
my class Algorisme:

[...]
class Algorisme(U,V) {
	string nom;
	uint versio;
	alias V function (U) Funcio;
	Funcio funcio;

	this(string nom, uint versio, Funcio funcio) {
		try {
			this.nom = nom;
			this.versio = versio;
			this.funcio = funcio;
		}
		catch {
			writeln("Error");
		}
	}

	string toString() {
		return format("%s (versió %s): %s -> %s", nom, versio, 
typeid(U), typeid(V));
	}

	Algorisme(U, V) opBinary(string op) (Algorisme(U, V) alg) {
		static if (op == '*') return new Algorisme(U,V)("composició", 
this.versio+alg.versio, this.funcio);
	}

}
[...]

but I receive these errors:

$ gdmd-4.6 algorisme.d
algorisme.d:31: function declaration without return type. (Note 
that constructors are always named 'this')
algorisme.d:31: no identifier for declarator Algorisme(U, V)
algorisme.d:31: semicolon expected following function declaration
algorisme.d:31: function declaration without return type. (Note 
that constructors are always named 'this')
algorisme.d:31: function declaration without return type. (Note 
that constructors are always named 'this')
algorisme.d:31: found 'alg' when expecting ')'
algorisme.d:31: no identifier for declarator 
opBinary(Algorisme(U, V))
algorisme.d:31: semicolon expected following function declaration
algorisme.d:31: Declaration expected, not ')'
algorisme.d:35: unrecognized declaration


Why it fails?
Anyone could help me?

Thanks,
Xan.