Self-Modifying code for user settings optimization

[Rikki Cattermole via Digitalmars-d]

interface IFoo {
	void a();
	void b();
}

__gshared IFoo a, b;
__gshared IFoo instance;

class Foo(bool bar) : IFoo {
	void a() {
		static if (bar) {
			// do something
		} else {
			// do nothing
		}
	}
}

shared static this() {
	a = new Foo!true;
	b = new Foo!false;
}

void update(Lookup lookup) {
	if (lookup["bar"])
		instance = a;
	else
		instance = b;
}

Small indirection when executing to find which function to execute but 
that is the best out of language semantics we have and only works for 
booleans.