Understanding generator expressions
CMake builds the solution in three stages – configuration, generation, and running the build tool. Generally, we have all the required data during the configuration stage. But every once in a while, we encounter the chicken and the egg problem. Take an example from the previous section – a target needs to know the path of a binary artifact of another target. But that information is only available after all the list files are parsed and the configuration stage is complete.
How do we deal with that kind of problem? We could create a placeholder for that information and postpone its evaluation to the next stage – the generation stage.
This is what generator expressions (sometimes called genexes) do. They are built around target properties such as LINK_LIBRARIES, INCLUDE_DIRECTORIES, COMPILE_DEFINITIONS, propagated properties, and many others, but not all. They follow rules similar to conditional statements and variable evaluation...
