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Subject: Re: [boost] Announcement: Faber, a new build system based on bjam
From: Hans Dembinski (hans.dembinski_at_[hidden])
Date: 2017-11-22 10:12:13


this is an answer to Richards mail, but I am mostly addressing Stephan.

> On 22. Nov 2017, at 09:00, Richard Hodges via Boost <boost_at_[hidden]> wrote:
> Stephan wrote:
>> In case it isn't obvious: I very much welcome collaboration, so if you
>> want to contribute (be it more tools or even entirely new
>> functionality), I'd be happy to talk.
> Nothing would please me more than to be able to dump the horrific syntax of
> cmake. I have often thought that python would be the obvious language for a
> replacement. There was of course a similar tool called SCONS once, which is
> python also. It seems to have fallen by the wayside.

I am not a big fan of CMake and I do like Python very much, but the success of CMake shows me once again that people have surprising needs they are usually not concerned about how powerful the tool is for the technical expert. Mostly it is about making simple things simple and saving time for the average guy.

Here is my list why I believe CMake is so popular (ordered by perceived priority):
1) it is a high-level language for describing build trees, it allows me to ignore much of the technical low-level stuff, like how to call the compiler with the right options
2) the commands have nice long names which makes CMake build scripts almost self-documenting
3) it ships with a maintained collection of scripts to configure and include external libraries
4) there is a company behind it which continuously adapts cmake to its user base and advertises its use
5) the documentation is ok
6) it is comparably fast (Scons was rejected because it is slow, AFAIK), especially when you use the Ninja backend
7) it has a ncurses-based configuration interface
8) it produces pretty output

Since cmake has already an impressive following, this adds the most important item on the top of the list:
0) people already know the tool and don't have to learn it

Boost.Build does not offer points 0-4 and 7 and neither does Faber, it seems. The Hello World example in the Faber docs reminds me a lot of Makefiles, because of the $(<) and $(>) syntax.
# define some actions
compile = action('c++.compile', 'c++ -c -o $(<) $(>)')
link = action('', 'c++ -o $(<) $(>)')

# bind artefacts to sources using the above recipes
obj = rule(compile, 'hello.o', 'hello.cpp')
bin = rule(link, 'hello', obj)
test = rule(action('run_test', './$(>)'), 'test', bin, attrs=notfile|always)

default = bin
This looks rather mathematical and abstract. I appreciate math, but many people don't. The syntax is very terse, which I think is not good. For build scripts, I think that Cmake has a point with its long and descriptive names. I touch a build script only very rarely. If I touch it very rarely, I want it to be very easy to read, because I forgot all the little details of how it works after a few months. I learned CMake basically by looking at build scripts from other people, not by studying a documentation from ground up. This is incredibly useful, nobody likes to study manuals.

We had this discussion about the pros and cons of CMake a while ago, and it seems that nobody loves it, but it still seems like a useful compromise for many people. I don't see how Faber can compete with this, and I would prefer if we move Boost to CMake.

Best regards,

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