Re: [boost] Cmake

Subject: Re: [boost] Cmake
From: Edward Diener (eldiener_at_[hidden])
Date: 2017-06-24 20:18:29

On 6/24/2017 2:53 PM, Robert Ramey via Boost wrote:
> On 6/24/17 11:42 AM, Edward Diener via Boost wrote:
>> On 6/24/2017 1:05 PM, Peter Dimov via Boost wrote:
>>> P F wrote:
>>>> https://github.com/pfultz2/boost-cmake-demo/tree/bcm-demo
>>>>
>>>> The library for Boost.System is just:
>>>>
>>>> bcm_boost_package(system
>>>>   VERSION 1.64
>>>>   SOURCES
>>>>     src/error_code.cpp
>>>>   DEPENDS
>>>>     assert
>>>>     config
>>>>     core
>>>>     predef
>>>> )
>>>
>>> This certainly looks cleaner. It needs to distinguish between public 
>>> and private dependencies but that's easy to fix. And of course 
>>> there's the question who will maintain the version and the dependency 
>>> list.
>>
>> Shouldn't this be generated on the fly ? The sources are all files in 
>> the library's 'src' subdirectory and the dependencies come from your 
>> own boostdep.
> 
> I don't see that this is possible.  Consider and example:
> 
> a) I have and application A which uses the boost::date_time library.
> b) But it doesn't serialize dates/times So it doesn't include the 
> date_time/serialization header
> c) So application is not dependent upon the serialization library
> d) And it doesn't have to include build / maintenance overhead that 
> including the serialization library would entail.
> 
> Later
> 
> a) I make application B which used the boost::date_time library
> b) Part of the app also serializes date_time data
> c) So it includes date_time/serialization header
> d) And must be linked with the serialization compiled libraries.
> 
> My point is that one cannot support the notion of dependencies between 
> libraries outside of the context of a particular application.
> 
> So dependencies will either have to specified/maintained by hand or one 
> will need a tool which does something like
> 
> dependencies A.cpp -> dependent libraries for application A
> dependencies B.cpp -> dependent libraries for application B

How is a library supposed to know what your application needs ? That is 
not its responsibility. Doesn't CMake allow manipulation of what an 
application needs at some higher level ? When I have used CMake to build 
LLVM/Clang it certainly allowed me to choose what I wanted for my 
particular build even though LLVM/CLang provide a whole slew of 
CMakeLists.txt files. If we cannot setup CMake pretty easily for Boost 
libraries so that the end-user can manipulate builds and tests for his 
needs our CMake setup will be worthless.

> 
> Robert Ramey