OvermindDL1 wrote:
On Wed, Sep 2, 2009 at 8:43 PM, Andrei Alexandrescu<andrei@metalanguage.com> 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.
Personally I would find it interesting as it can hold extended data, but perhaps it would be nice to fold someway so it takes less data, perhaps one bit per sub-optional used up to the overall max of a char or int or something (would anyone really have 8 optionals embedded?)
I think, if folding should be supported then it should be done through an external metafunction, something like: typedef typename fold_optionals< T, 7 >::type single_optional; I think, the default behavior of optional should stay as is.