Using cmake options in generator expressions

Question

I would like to use a cmake option inside a generator expression in order to turn on a certain compile flag. From the documentation it is not clear to me how to achieve this.

I would like to write something like

option(MYOPTION " ... " OFF)
...
add_compile_options($<$<MYOPTION>:-lblas>)

which does not work.

Is there a way to achieve this?

Answer 1

Your example doesn't really specify a use case for this, and I think there are other ways of going about it (as well as -lblas being a linker flag not a compile option.) Just off of the information you provide, it looks like what you might want is:

option(MYOPTION "My Option" OFF)
...
add_compile_options($<$<BOOL:${MYOPTION}>:-lblas>)
#(or maybe you want?)
target_compile_definitions(YOUR_TARGET PRIVATE $<$<BOOL:${MYOPTION}>:-lblas>)

$<$<BOOL:...>:...> needs a variable to assist with evaluating (which MYOPTION fulfills. There are other logical expressions listed in the documentation that you may use.