[CMake] Feature request: generic (config-like) selector on target_link_libraries

[Alexandre Feblot]

Specifying the lib4 dependency in the exe? But what about dependencies
order in the link line? In my example, lib4-A or lib4-B must appear
after lib3, if I want lib4 symbols required by lib3 to be added. In your
solution, lib4 might as well be added by cmake just after lib1 and
before lib3, which will result in a link failure.
More over, the executable is even not supposed to know that it depends
on lib4. It just knows it depends on lib1, which knows it depends on
lib3, which knows it depends on lib4. (I gave a simple example, but the
real project is a large one with many dependencies, including circular
ones, and we don't want / can't easily know all libX-A/B that must be
added to every executable)


Also, tell me if I'm wrong, but I don't see how the if-then-else
solution could be used: the build occurs in a single project which
builds all libraries and executables. That means that lib3 must depend
on lib4-A or lib4-B according to the executable we link. Using
it-then-else would only add a dependency to one the lib4 version, and
that could not be changed afterwards when linking my binaries: for some
of them, lib3 must depend on lib4-A, and for some others, the same lib3
must then depend on lib4-B.


Regards,
Alexandre

-----Original Message-----
From: Michael Wild [mailto:themiwi at gmail.com] 
Sent: Tuesday, 24 March 2009 13:43
To: Alexandre Feblot
Cc: Cmake Mailing List
Subject: Re: [CMake] Feature request: generic (config-like) selector on
target_link_libraries


On 24. Mar, 2009, at 12:30, Alexandre Feblot wrote:
>
> Dependency graph example: "->" means "depends on"
>
> exe1-A -> lib1 -> lib3 -> lib4-A -> lib5 -> lib7
> exe1-B -> lib1 -> lib3 -> lib4-B -> lib6 -> lib8
> exe2-A -> lib2 -> lib3 -> lib4-A -> lib5 -> lib7
> exe2-B -> lib2 -> lib3 -> lib4-B -> lib6 -> lib8
>
>> I'd like to keep using the standard cmake mechanism of dependency
> description in which every lib only defines on which other libs it
> depends, and let cmake compute the final link line.
>

I also fail to see why this would be a problem, especially if all  
libraries are static, as you say (Static libraries are simply archives  
of object files, so no symbols have to be resolved while they are  
created since no linking happens). Simply don't have lib3 depend on  
any of the lib4-X, but add those lib4-X directly to the link-commands  
of exeY-X.

E.g.:

# Establish dependencies between static libraries.
target_link_libraries( lib1 lib3 )
target_link_libraries( lib2 lib3 )
target_link_libraries( lib5 lib7 )
target_link_libraries( lib6 lib8 )
target_link_libraries( lib4-A lib5 )
target_link_libraries( lib4-B lib6 )

# Link the executables
target_link_libraries( exe1-A lib1 lib4-A )
target_link_libraries( exe1-B lib1 lib4-B )
target_link_libraries( exe2-A lib2 lib4-A )
target_link_libraries( exe2-B lib2 lib4-B )

Hope this helps

Michael


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