ConstaddHandlerFor('clone', FooClass, (original, seen) => new FooClass(original.bar, original.baz));
addHandlerFor('equals', FooClass, (a, b, seen) => equals(a.bar, b.bar, seen) && equals(a.baz, b.baz, seen));
addHandlerFor('merge', FooClass, (target, source, opts) => merge(target.bar, source.bar, opts));
Add a handler for a specific function