>> Curiously if you create holder like this, it will give an
>> arrayoutofbound error at runtime, I don't know if that is a bug:

Yep, variants are cool. You could even use an struct as value type of the
associative array and store the variant in one member and the signature
of the delegate, as string, in another member. The you could use a mixin
in the receiver to extract the delegate without knowing the original
signature.

All this is  wonderfully disturbing to me :)