[CMake] Referencing an OBJECT library

[Petr Kmoch]

Hi Edward.

"the reference to that OBJECT library is through $<TARGET_OBJECTS:xxx>" -
that is not quite true. When you're referring to the object library target
itself (e.g. reading its properties), you use its name just like with any
other target:

  get_property(someVar TARGET xxx PROPERTY TYPE)

However, the genex $<TARGET_OBJECTS:xxx> is used when you're specifying
that the sources of another target yyy are to include the objects
comprising the object library xxx:

  add_executable(yyy main.cpp $<TARGET_OBJECTS:xxx>)

Here, you're not dealing with the object library xxx itself, but with the
objects from which it's composed, so you're referring to these objects
explicitly. It's quite similar to how you'd use other properties of a
target:

  target_sources(yyy $<TARGET_PROPERTY:xxx,SOURCES>)

would similarly add all sources of target xxx to the target yyy.

Petr

On 20 July 2017 at 22:57, Edward Diener <eldlistmailingz at tropicsoft.com>
wrote:

> According to the CMake docs for an OBJECT library called, let's say,
> 'xxx', the reference to that OBJECT library is through
> $<TARGET_OBJECTS:xxx>. I understand this but I am curious about the reason
> for such syntax. After all a STATIC or SHARED library 'xxx' you can just
> use xxx to refer to the library. Why the difference in CMake syntax
> reference between OBJECT libraries added with the add_library command and
> STATIC or SHARED libraries added with the add_library command ?
>
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