On Wed, Sep 2, 2009 at 8:52 PM, Joel de Guzman<joel@boost-consulting.com> wrote:
Andrei Alexandrescu wrote:
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 thought I'd ask here because by now there's a significant body of experience with optional<T>. I perused the online documentation and the forum and couldn't find information about that specific detail.
We use boost.optional extensively in Boost.Spirit. IIRC, we collapse such things. Usually they occur in generic code. I see no real need for optional<optional<T>>. If there's a use for it, I too would like to hear it.
Slightly off-topic, but I consider D to be a *fascinating* language, kind of like how C++ should have been. It would actually be *much* easier to create Spirit in D then it would have been in C++, and you could have used real PEG syntax instead of C++/D'ifying it. I never really played around with D due to the lack of a Visual Assist quality IDE for it though, but I have read through the language spec (much better read then C++'s) multiple times just for the heck of it, and it is absolutely fascinating! Kind of bugs me that it has two 'generic' libraries that do the same things in different ways though, and you cannot mix code that uses both...