Hi Andrei,
Hello,
I'm defining an "optional" type for D's standard library modeled similarly to Boost.optional. An interesting question came up - should optional<optional<T>> fold itself into optional<T>, or is "double optional" an interesting concept of its own?
I guess it depends on the context where the recursive optionals would appear. Clearly, you can only fold while the initialization state is the same. That is, if the outer optional<> is initialized but the inner is not, then you can't fold it. OTOH, for a run of consistently initialized optionals, folding could make sense. But then again it still depends on the context: if the very *structure* of the recursion matters, the folding would be wrong. So, I would allow optionals to recurse AND provide an explicit function/method to "reduce" a given recursive optional as far as possible (i.e. up to the point the initialization state changes) HTH -- Fernando Cacciola SciSoft Consulting, Founder http://www.scisoft-consulting.com