Generator Expressions Compile Options target_compile_options(hello PRIVATE $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>,$<CXX_COMPILER_ID:GNU>>: -Werror -Wall -Wextra> $<$<CXX_COMPILER_ID:MSVC>: /W4> )