[CMake] How to describe lib dependencies when a lib has different possible implementations?

[Christopher Harvey]

Hi,
Interesting question. You said that
"only one of them has to be used in every executable, the implementation 
to use is determined by the executable."
These are static libraries, so how can the exec pick one if it isn't 
even built? (As opposed to loading one dynamically)
Basically I'm still wondering at what point you want the decision for 
one of the two libraries to made and how you make that decision.
How exactly did you do it beforehand, without cmake?
CMake has IF statements, so I'm pretty sure it'll be no problem just 
have no idea what you would put in those ifs.

Chris.

Alexandre Feblot wrote:
> Hi,
>  
> I'm facing an issue while trying to port my current build system to 
> cmake and don't know is there is a way to solve it:
>  
> In our project, we build a bunch of *static* libs (about 360) and 
> several executables on them.
>  
> * one library, in the middle of the lib dependency chain, has in fact 
> 2 different implementations. That is to say, there are 2 different 
> libs with the exact same interface, but they don't use the same 
> back-end, have different source code, and don't have the same 
> dependencies.
> * only one of them has to be used in every executable, 
> the implementation to use is determined by the executable.
>  
> 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.
>  
> The question is: how can I express the dependencie of lib3 on 
> lib4 whereas lib3 has only a single description, and we don't know 
> when describing it, if we'll have to use lib4-A or lib4-B. (and 
> anyway, depending on the executable, we'll have to use each of them).
>  
> Is there any concept of "abstract" target (lib4 in my example) which 
> could be "instanciated" in the executable description (as lib4-A or 
> lib4-B in the example)
>  
>  
> Thanks,
>  
> Alexandre
>  
>
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