Tutorial: Maybe mistake in Step2
After pass Step2, we will get a CMakeLists.txt does not contain "EXTRA_LIBS" or "EXTRA_LIBS", which will be removed in Step3. It's different with https://cmake.org/cmake/help/book/mastering-cmake/cmake/Help/guide/tutorial/index.html#adding-a-library-step-2. In above site, we can find that
if(USE_MYMATH)
add_subdirectory(MathFunctions)
list(APPEND EXTRA_LIBS MathFunctions)
list(APPEND EXTRA_INCLUDES "${PROJECT_SOURCE_DIR}/MathFunctions")
endif()
which refers to the code will be removed in Step3.
This artical is confusing.