Re: [jamboost] Redundant project ID assignment

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-12-27 05:19:35

On Monday 27 December 2004 12:38, David Abrahams wrote:
> The tutorial, in section bbv2.tutorial.libs, suggests first adding a
> project id "foo" to top/util/foo/Jamfile:
>
> project foo
>
> : usage-requirements <include>.
>
> ;
>
> And then adding to top/Jamfile:
>
> use-project /foo : util/foo ;
>
> These declarations seem to me to be entirely redundant -- they both
> associate the project id /foo with the top/util/foo/Jamfile. Why should
> both be needed? 

Theoretically, there's no such need, and we've agreed to change that.

> What currently happens if only one of them is supplied? 

It's not allowed.

I think the only function of project id in the "project" rule is to allow 
subprojects of a given project root to use project ids without "use-project".

Say: Jamroot:

build-project libs/a ;
build-project libs/b ;

libs/a/Jamfile:

project boost/a ;
lib a ;

libs/b/Jamfile

lib b : b.cpp /boost/a//a ;

Without project ids, Jamroot would have to be:

use-project /boost/a : libs/a ;
use-project /boost/b : libs/b ;

which is a bit inconvenient -- after all, the project in libs/a can define a 
project id itself.

In fact, it's not clear if we should drop id in project or in 
use-requirements. Most of the time I want to use "boost at /home/ghost/boost" 
and don't want to rename any ids. So, maybe the right syntax is:

Jamroot for boost:

project boost ;

Some Jamfile:

use-project-at /home/ghost/boost ; 
# Makes "boost" project id available in this Jamfile

- Volodya