Re: [boost] [CallableTraits] The formal review begins today

Subject: Re: [boost] [CallableTraits] The formal review begins today
From: Edward Diener (eldiener_at_[hidden])
Date: 2017-04-05 23:12:07

On 4/3/2017 2:45 AM, Louis Dionne via Boost wrote:
> Dear Boost community,
>
> The formal review of Barrett Adair's CallableTraits library begins today,
> 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, and
>   conditions for acceptance if any
> - Your name
> - Your knowledge of the problem domain
>
> You are strongly encouraged to also provide additional information:
> - What is your evaluation of the library's:
>   * Design
>   * Implementation
>   * Documentation
>   * Tests
>   * Usefulness
> - Did you attempt to use the library? If so:
>   * Which compiler(s)?
>   * What was the experience? Any problems?
> - How much effort did you put into your evaluation of the review?
>
> We await your feedback!

The documentation is confusing regarding the level of C++ conformance 
needed to use the library. At the beginning it says that the library is 
a C++11/C++14/C++17 library, whatever this means. Later information 
explains that it is only dependent on a C++11 standard library. There is 
mention of compatibility claims, which further confuses the issue. 
Finally there is mention of static asserts or substitution failures for 
some functionality.

Frankly with all this confusion I would be very loath to use the library 
as the doc explains the issue(s). It would be much clearer if the 
library expressed the minimum level of C++ compliance needed for the 
majority of the functionality and then documented any greater level of 
C++ conformance needed for specific functionality. Also the library 
should document a standard behavior when the level of conformance is not 
met, either internal adjustment to a lower level of conformance, 
compiler errors, static asserts, or run-time exceptions, depending on 
how the library is designed, and these need to be carefully explained if 
they differed for different functionality.

The number 3) item in comparing callable traits to the current Boost 
function types needs more explanation. Having used Boost function types 
in code ( Boost tti uses it, and I have used it in other programming 
endeavors ) I do not see how the callable traits library author could 
think that Boost function types encourages template specializations, so 
maybe an example showing what is meant by item 3) would be needed to 
back up this claim. Please note: I am certainly not against modernizing 
the function type interface; I just think that claims vis a vis Boost 
function types need to be backed up with actual proof by example.