Re: [boost] CMake Modularization

Subject: Re: [boost] CMake Modularization
From: Peter Dimov (lists_at_[hidden])
Date: 2016-10-02 21:22:00

Paul Fultz II wrote:
> Instead a top-level cmake can bring the packages together, something like:
>
>     set(BOOST_ALL TRUE)
>     # Whatever cmake modulues boost provide
>     include(cmake/BoostModules.cmake)

Something like that, although BOOST_ALL does not strike me as quite correct 
a name, I'd call that BOOST_IS_LOCAL. (It doesn't have to be all of Boost, 
could be a subset.)

We'll probably also need

set(BOOST_ROOT ${CMAKE_SOURCE_DIR})

>     # Include the libraries
>     # Perhaps this could be globbed
>     add_subdirectory(libs/fit)
>     add_subdirectory(libs/hana)

It has to be globbed, for the same reason. Subsets should be supported.

> Then in the library, the cmake would do something like this:
>
>     # We are building standalone
>     if(NOT BOOST_ALL)
>         # BoostModules must be installed first, before building standalone
>         find_package(BoostModulues)
>     endif()
>
>     # Find the dependent boost libraries
>     find_boost_lib(BOOST_LIBS asio hana)
>
> So now, when building standalone `find_boost_lib` will call `find_package` 
> to retrieve the exported targets. If its building in-tree, then 
> `find_boost_lib` will just find the target name, and let cmake resolve the 
> target during build.

Yes, this could work for possibly-standalone libraries.