Re: [boost] [CMake] what to do now?

Subject: Re: [boost] [CMake] what to do now?
From: Robert Ramey (ramey_at_[hidden])
Date: 2016-04-14 21:47:15

On 4/14/16 4:02 PM, Andrey Semashev wrote:

> I think you misunderstood me. You can build sources, docs and tests
> separately. You can place CMakeLists.txt at the places where Jamfiles
> currently are. Each of these CMakeLists.txt would declare their own
> project and could be independent from others.
>
> However, the common practice is a bit different. There is typically a
> single root CMakeLists.txt, which defines a project and then includes a
> number of nested CMakeLists.txt. The nested CMakeLists.txt may or may
> not define their projects, that doesn't really matter if you invoke
> cmake with the root CMakeLists.txt because you're generating makefiles
> for the whole tree in this case. You can also build targets selectively
> in this case.

My understanding is quite different.

In each directory one has a CMakeLists.txt file.  This would closely 
correspond to current boost practice.

In addition in the parent directory one creates a CMakeLists.txt 
directory.  It's primary function is to factor common CMake commands 
corresponding to the child directories.  It includes a statement 
add_directory(<child directory name>) for each subdirectory.
Then when you CMake the parent all the children are "CMaked" after 
having processed the common code in the parent.  As it stands this makes 
sense.  But if you include common CMake commands in the parent you won't 
be able to run CMake on the subdirectories.  So if you want to that, 
just refrain from factoring common code in the parent directory CMake. 
I believe that CMake has an "include" facility so you could have it both 
ways - start from the parent or the children.

CMake has a few issues.

The documentation is very extensive - but really consists of just a 
reference to the CMake functions one can call.  There is no overall 
sense of how the whole thing is supposed to work.  There is a lot of 
information on stack overflow, etc to fill this gap.  But most find a 
way that works and presume that everyone does it that way.  Truth is 
there is not "canonical" way to do it - but everyone thinks there is and 
that they know what it is.  Very confusing.  I spent a lot of time 
studying the system in order to make my "CMake for dummies" cheat sheet 
which I included in the Boost Library Incubator.  I described the 
simplest system which would work for a simple boost library - header 
only.  My goal was simplicity.  If I had nothing else to do I would 
expand upon it.  But I don't so I can't

Robert Ramey

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