Re: [boost] Boost CMake support - Request for Comment

Subject: Re: [boost] Boost CMake support - Request for Comment
From: Edward Diener (eldiener_at_[hidden])
Date: 2018-10-16 14:12:40

On 10/16/2018 3:34 AM, Alexander Grund via Boost wrote:
> 
>> For Predef 
>> <https://github.com/boostorg/predef/tree/develop/tools/check> with 
>> documentation for usage here 
>> <https://www.boost.org/doc/libs/1_68_0/doc/html/predef/check_utilities.html>. 
>>
>>
>> For Config <https://github.com/boostorg/config/tree/develop/checks> 
>> and documentation for that here 
>> <https://www.boost.org/doc/libs/1_68_0/libs/config/doc/html/boost_config/build_config.html>. 
>>
> Thanks. Seeing this I approximate the work required to convert the 
> checks of Config to ~1h, maybe 2h. Usage would be:
>  Â  include(BoostConfigFeatures)
>  Â  if(BOOST_FEATURE_cxx11_local_class_template_parameters)
>  Â Â Â  add_executable(...)
>  Â  endif()

Programmers are notorious for estimating the work to do any programming 
as about an order of magnitude less than it really takes <g>.

> 
> Some bike-shedding required:
> - Name for the CMake file that contains this

Anything reasonable with 'config' in the name for config and 'predef' in 
the name for predef.

> - Naming scheme for the results of the checks (the variable in the "if")

As close as possible, using CMake naming conventions, to the name in 
config or predef.

> - Eagerly test all or on demand:

What is the difference in CMake terms ? In Boost Build I am fairly sure 
the checks are done on demand, and usually involves some sort of 
compile/build/run/test-result cycle which would make pre-testing all 
checks in a library, and holding the result for further inquiry, pretty 
expensive.

>  Â  boost_config_has(RESULT cxx11_local_class_template_parameters)
>  Â  if(RESULT) add_executable(...) endif()
> 
> Similar for predef:
>  Â  include(BoostPredefCheck)
>  Â  boost_predef_check(RESULT "BOOST_OS_WINDOWS != 0" "BOOST_OS_VMS != 0")
>  Â  if(RESULT) add_executable(...) endif()
> 
> Work is about the same and yes some checks can be omitted (e.g. 
> boost_predef_check(RESULT "BOOST_OS_WINDOWS != 0") --> RESULT==WIN32 
> standard CMake variable)

Even if there is a standard CMake variable it would be worthwhile to 
have the check so that libraries which use the check can use the same 
syntax throughout.