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Subject: Re: [boost] trunk vs release
From: Bjørn Roald (bjorn_at_[hidden])
Date: 2009-06-03 17:12:55

On Wednesday 03 June 2009 09:30:01 pm Vladimir Prus wrote:

> Can you use git-submodule to implement this layout:
> libs/
> program_options/
> includes/
> boost/
> program_options [ same content as includes above, even as
> 'includes' is modified]

I don't think that is something git submodules is well suited for. I doubt
svn externals are any good either. That looks like something you need file
system support for, aka symbolic links. Otherwise you need to run some
command to ensure the directories are in sync. If you can not use the file
system to ensure the content is identical, then you should select the command
with some care.

Build system commands, not source control system commands, seems logical. The
build system need to ensure the sync of headers for the build anyway.
Furthermore, build systems are good at avoiding unnecessary modifications of
derived objects (target files). This is very important as build time would
suffer from any simpler logic. An implicit or explicit copy rule in the build
system for each header comes to mind. I know this to be a successful scheme
in large build systems. Such builds generally consist of 2 passes:

pass 1 - whenever needed, the build system:
        generate code (if you have code generation in build)
        copy public headers from source controlled location to the public location
pass 2 - whenever needed, the build system:
         compile (against public location and component local headers only)

This can be performed per sub-projects (components) if you have good
dependency tracking between sub-projects. Otherwise it may be wise to
complete pass 1 for all sub-projects before starting any pass 2 build tasks.

commands like:

> bjam pass1

could be supported to update public headers without performing full build.

Note also that such a build system "header copy" scheme, open some other
possibilities that may be of interest as boost grows, which I do not dig into

A file system based solution is much simpler, but I am not sure that is
feasible as it probably is hard to do this in a portable way. You can do that
in ClearCase as that SCM system comes with its own virtual file system for all
development platforms.

Bjørn Roald

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