Re: [boost] Announcing CallableTraits' formal review next week (April 3rd)

Subject: Re: [boost] Announcing CallableTraits' formal review next week (April 3rd)
From: Zach Laine (whatwasthataddress_at_[hidden])
Date: 2017-04-08 18:09:47

On Mon, Mar 27, 2017 at 11:38 PM, Louis Dionne via Boost <
boost_at_[hidden]> wrote:

> Dear Boost community,
>
> The formal review of Barrett Adair's CallableTraits library starts Monday,
> April 3rd and ends on April 12th.
>
>   CallableTraits is a C++11 library for the inspection, synthesis, and
>   decomposition of callable types. CallableTraits aims to be the "complete
>   type manipulation facility for function types" mentioned in the final
>   paragraph of C++17 proposal P0172, and removes the need for template
>   specializations for different function signatures.
>
> You can find the documentation of the library here:
>
>   http://badair.github.io/callable_traits/doc/html/index.html
>
> and the GitHub repository here:
>
>   https://github.com/badair/callable_traits
>
> We encourage your participation in this review. At a minimum, kindly state:
> - Whether you believe the library should be accepted into Boost
>

Yes.

> - Your name
>

Zach Laine

> - Your knowledge of the problem domain
>

I am reasonably knowledgable.  I do extensive metaprogramming from time to
time, though this is not my specialty.

> You are strongly encouraged to also provide additional information:
> - What is your evaluation of the library's:
>   * Design
>

This seems good to me.  There's one thing I consider to be a glaring
omission, though.  I would love to have pre-17 versions of these traits:

template <class Fn, class... ArgTypes>
struct is_invocable;
template <class R, class Fn, class... ArgTypes>
struct is_invocable_r;
template <class Fn, class... ArgTypes>
struct is_nothrow_invocable;
template <class R, class Fn, class... ArgTypes>
struct is_nothrow_invocable_r;

>    * Implementation
>

I did not look at the implementation.

>   * Documentation
>

>From the first page of the docs, this:

"
The use cases for CallableTraits overlaop significantly with those of
Boost.FunctionTypes
<http://www.boost.org/doc/libs/1_61_0/libs/function_types/doc/html/index.html>.
Here are some reasons why you might prefer CallableTraits over the latter:
"

is awkward enough that I had to re-read it.  It mentions two things, but in
the order A B A, then uses "latter", which is off-putting.  Can I suggest
instead:

"
The use cases for CallableTraits overlap significantly with those of
Boost.FunctionTypes
<http://www.boost.org/doc/libs/1_61_0/libs/function_types/doc/html/index.html>.
Here are some reasons why you might prefer CallableTraits:
"

Also, "overlaop" is a typo. :)

I also find it odd that the FAQ immediately follows the intro page.  I
think this would be better placed before the Contact section.  Keeping it
where it is now disturbs the flow of the reader's thinking when getting to
know the library for the first time (or at least it did so for me).

Nearly every section of the reference docs says this:

"
Compatibility Notes

Full support on GCC 4.7.4+, Clang 3.5+, Visual Studio 2015, and XCode 6.4+.
"

This is not a problem per se, but it's noise considering that the same
statement is made in the intro section.  I think the reference entry should
only contain such a notice *only* when it differs from the general note
from the intro.  This has the benefit of being clearer -- I won't see the
note above and wonder if it differs slightly from the general intro note.

  * Tests
>

They seem to provide decent coverage, and line up with the documented
semantics.  The docs in fact seem to use quoted test code to illustrate
behavior, which is nice.

>   * Usefulness
>

Very useful.  As someone who is not a metaprogramming specialist, I often
need facilities like this when doing MP, and I often define my versions
with subtle defects.

> - Did you attempt to use the library?
>

Not really.  I only ran the tests on Clang 3.9.

- How much effort did you put into your evaluation of the review?
>

About 5 hours.

Zach