CMake/Help/guide/tutorial/Step4/MathFunctions/CMakeLists.txt

# create the MathFunctions library
add_library(MathFunctions MathFunctions.cxx)

# state that anybody linking to us needs to include the current source dir
# to find MathFunctions.h, while we don't.
target_include_directories(MathFunctions
                           INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
                           )

# should we use our own math functions
option(USE_MYMATH "Use tutorial provided math implementation" ON)
if (USE_MYMATH)
  target_compile_definitions(MathFunctions PRIVATE "USE_MYMATH")

  # library that just does sqrt
  add_library(SqrtLibrary STATIC
              mysqrt.cxx
              )

  # link our compiler flags interface library
  target_link_libraries(SqrtLibrary PUBLIC tutorial_compiler_flags)
  target_link_libraries(MathFunctions PUBLIC SqrtLibrary)
endif()

# link our compiler flags interface library
target_link_libraries(MathFunctions PUBLIC tutorial_compiler_flags)