[CMake] help with OBJECT libraries hierarchy

[Petr Kmoch]

Ahoj Miro,

object libraries are not intended for linking. The way it works is you
expand the $<TARGET_OBJECTS> genex into the list of *sources* of the
consuming target. In other words, the string '$<TARGET_OBJECTS:main>' needs
to go into the add_executable(foo) or add_library(foo) command, not into
target_link_libraries(foo).

Petr

On 22 June 2016 at 12:47, Ilias Miroslav <Miroslav.Ilias at umb.sk> wrote:

> Dear experts,
>
>
> I am trying to introduce OBJECT libraries into our project,
> http://www.diracprogram.org. <http://www.diracprogram.org>
>
>
> Into local src/functionality1/CMakeLists.txt I changed
>
>
> add_library(main ${local_sources})
>
>                     to
>
> add_library(main  OBJECT ${local_sources})
>
>
> at  higher level, in src/CMakeLists.txt I changed
>
>
> add_subdirectory(${PROJECT_SOURCE_DIR}/src/functionality1)
> set(EXTERNAL_LIBS main ${EXTERNAL_LIBS})
>
>                                    to
>
> add_subdirectory(${PROJECT_SOURCE_DIR}/src/functionality1)
> set(EXTERNAL_LIBS  $<TARGET_OBJECTS:main> ${EXTERNAL_LIBS})
>
>
> and at the highest level of our CMake infrastructure I have linking of all
> object libraries for given  executable(s) :
>
>
>  target_link_libraries( ${_executable}  ${EXTERNAL_LIBS}  )
>
>
> However, during configuration I am getting repeating error messages  of
> type
>
>
> "CMake Error at cmake/custom/core.cmake:75 (target_link_libraries):
>   Error evaluating generator expression:
>
>     $<TARGET_OBJECTS:main>
>
>   The evaluation of the TARGET_OBJECTS generator expression is only
> suitable
>   for consumption by CMake.  It is not suitable for writing out elsewhere.
> Call Stack (most recent call first):
>   CMakeLists.txt:77 (include)"
>
> Any help please how to best arrange OBJECT libraries ? I have cmake
> version 3.5.0 .
>
>
> Yours, Miro
>
>
>
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