On Fri, Jul 21, 2017 at 10:36 AM, Bjorn Reese via Boost < boost@lists.boost.org> wrote:

The formal review of Peter Dimov's Mp11 library is scheduled for July 15 - July 24, 2017 [1].

Mp11 is a C++11 metaprogramming library for compile-time manipulation of data structures that contain types. It’s based on template aliases and variadic templates and implements the approach outlined in the article "Simple C++ metaprogramming" [2] and its sequel [3]. These articles are useful background information for the review.

I want to say something up front about my bias that may be useful to the review manager. I do (and have done) a significant amount of metaprogramming (TMP specifically). I've almost always done it in the context of SFINAE-constraining a template or computing the return type of a function. I've never needed a compile-time set or map. Parameter packs or other type lists have always been sufficient for my needs, and I use those somewhat infrequently.

* Mp11 aims to make simple usage simple, and to support complex usage without complicating the simple use cases.

I don't need mp11 or anything like it for simple cases; among those of us who do TMP, simple things are now (meaning in C++ >=14) trivial. It seems to be a very nice fit for the more complex ones.

* Mp11 works on any type-list, whether its own type-list mp_list, or standard type-lists such as std::tuple and std::variant, or user-defined type-lists.

* Mp11 works with any meta-function, such as C++11 or Boost type-traits, or user-defined type-traits.

Both of these points are borne out by my experiments with the library, and are great to see. The whole point of a library is code reuse, right?

Mp11 can be found here:

* Documentation: https://rawgit.com/pdimov/mp11 /master/doc/html/mp11.html

* Source code: https://github.com/pdimov/mp11/tree/master

Please answer the following questions in your review [4]:

1. Should Mp11 be accepted into Boost? Please state all conditions for acceptance explicity.

Yes, I vote to accept. No conditions.

2. What is your evaluation of the design?

The design is very nice. I especially like the interoperability with arbitrary type sequences and metafunctions mentioned above. However, if the library is targeting eventual standardization, it should either target the needs of C++ >=20 (with if constexpr and probably concepts), or should at least have a portion of it that does, so that part can be proposed as a standalone entity with usage experience. 3. What is your evaluation of the implementation?

It seems very straightforward and easy to follow (though I did not look at all of it).

4. What is your evaluation of the documentation?

A lot of people have complained that there isn't enough of it, but I found it to be just right. Perhaps it's a bit Spartan for non-TMP folks, but why do they want to use it? Perhaps inlining the "Simple C++ metaprogramming" articles would help? Is mp11 intended to be used as a direct replacement for mpl? If so, a brief discussion of that would be useful in the docs. Specifically, how one might convert existing mpl-using code to use mp11. 5. What is your evaluation of the potential usefulness of the library?

For me, very low. I am convinced that others can get a lot of use out of the more complex features, like the set and map operations. I would also be more convinced to use it if I knew where it fit in the metaben.ch rankings. 6. Did you try to use the library? With what compiler? Did you have

any problems?

Yes. I tried to use just a few of the list operations and algorithms with Clang 4. No problems.

7. How much effort did you put into your evaluation? A glance? A quick reading? In-depth study?

I read all the docs (that was fast :), and spent an hour or so playing with the code.

8. Are you knowledgeable about the problem domain?

Yes. Zach