On 5/5/2014 11:03 AM, Rein Halbersma wrote:

Hi everyone, this is my first post to this mailinglist, so I hope I follow the proper conventions around here (yes, I did read the Discussion Policy).

I have a small feature request for the Type Traits Introspection library: a macro BOOST_TTI_BOX_TYPE(U) that defines a class template box_type<T> with a nested typedef named "type" that equals T::U.

Rationale: because box_type<T> is a metafunction that can be supplied to mpl::eval_if, this facilitates user-defined traits that extract a nested type U, but can fall back to a (user-defined) default type. This mimics the C++11 allocator_traits that also provide defaults for allocators that lack certain nested typedefs or other properties.

Small self-contained example: http://coliru.stacked-crooked.com/a/76b9abf4aaf00350

One could probably also define similar "boxing" macros to go along with the has_template and other introspection tools in TTI.

Would this be considered a useful feature?

Could you look at the documentation for BOOST_TTI_MEMBER_TYPE in the section called "Nested Types" of the TTI documentation ? I think you can easily adapt this to the purposes of your example.

On May 5, 2014 11:03:01 AM EDT, Rein Halbersma wrote:

I have a small feature request for the Type Traits Introspection library: a macro BOOST_TTI_BOX_TYPE(U) that defines a class template box_type<T> with a nested typedef named "type" that equals T::U.

Where does the macro get T?

Small self-contained example: http://coliru.stacked-crooked.com/a/76b9abf4aaf00350

Posting the code facilitates later searching and prevents problems on finding out later (should the linked site disappear or the linked code be deleted on the future). It also permits quoting portions in replies. ___ Rob (Sent from my portable computation engine)