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Tutorial: Improve Step 10 generator expression example.
Use compiler flags and standard levels as the compelling argument for using generator expressions and interface libraries
This commit is contained in:
Robert Maynard
committed by
Brad King
Brad King
parent
a1c6d7e9af
commit
fa203ee323
@@ -1,8 +1,17 @@
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cmake_minimum_required(VERSION 3.3)
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cmake_minimum_required(VERSION 3.15)
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project(Tutorial)
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set(CMAKE_CXX_STANDARD 11)
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set(CMAKE_CXX_STANDARD_REQUIRED True)
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add_library(tutorial_compiler_flags INTERFACE)
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target_compile_features(tutorial_compiler_flags INTERFACE cxx_std_11)
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# add compiler warning flags just when building this project via
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# the BUILD_INTERFACE genex
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set(gcc_like_cxx "$<COMPILE_LANG_AND_ID:CXX,ARMClang,AppleClang,Clang,GNU>")
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set(msvc_cxx "$<COMPILE_LANG_AND_ID:CXX,MSVC>")
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target_compile_options(tutorial_compiler_flags INTERFACE
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"$<${gcc_like_cxx}:$<BUILD_INTERFACE:-Wall;-Wextra;-Wshadow;-Wformat=2;-Wunused>>"
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"$<${msvc_cxx}:$<BUILD_INTERFACE:-W3>>"
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)
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# set the version number
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set(Tutorial_VERSION_MAJOR 1)
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@@ -21,6 +21,7 @@ if(USE_MYMATH)
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# first we add the executable that generates the table
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add_executable(MakeTable MakeTable.cxx)
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target_link_libraries(MakeTable tutorial_compiler_flags)
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# add the command to generate the source code
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add_custom_command(
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@@ -44,14 +45,18 @@ if(USE_MYMATH)
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POSITION_INDEPENDENT_CODE ${BUILD_SHARED_LIBS}
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)
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target_compile_definitions(SqrtLibrary PRIVATE
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"$<$<BOOL:${HAVE_LOG}>:HAVE_LOG>"
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"$<$<BOOL:${HAVE_EXP}>:HAVE_EXP>"
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)
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target_link_libraries(SqrtLibrary PUBLIC tutorial_compiler_flags)
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target_compile_definitions(MathFunctions PRIVATE "USE_MYMATH")
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if(HAVE_LOG AND HAVE_EXP)
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target_compile_definitions(SqrtLibrary
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PRIVATE "HAVE_LOG" "HAVE_EXP")
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endif()
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target_link_libraries(MathFunctions PRIVATE SqrtLibrary)
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endif()
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target_compile_definitions(MathFunctions PRIVATE "$<$<BOOL:${USE_MYMATH}>:USE_MYMATH>")
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target_link_libraries(MathFunctions PUBLIC tutorial_compiler_flags)
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# define the symbol stating we are using the declspec(dllexport) when
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# building on windows
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@@ -62,7 +67,7 @@ set_property(TARGET MathFunctions PROPERTY VERSION "1.0.0")
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set_property(TARGET MathFunctions PROPERTY SOVERSION "1")
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# install rules
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install(TARGETS MathFunctions
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install(TARGETS MathFunctions tutorial_compiler_flags
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DESTINATION lib
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EXPORT MathFunctionsTargets)
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install(FILES MathFunctions.h DESTINATION include)
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@@ -1,8 +1,17 @@
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cmake_minimum_required(VERSION 3.3)
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cmake_minimum_required(VERSION 3.15)
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project(Tutorial)
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set(CMAKE_CXX_STANDARD 11)
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set(CMAKE_CXX_STANDARD_REQUIRED True)
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add_library(tutorial_compiler_flags INTERFACE)
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target_compile_features(tutorial_compiler_flags INTERFACE cxx_std_11)
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# add compiler warning flags just when building this project via
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# the BUILD_INTERFACE genex
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set(gcc_like_cxx "$<COMPILE_LANG_AND_ID:CXX,ARMClang,AppleClang,Clang,GNU>")
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set(msvc_cxx "$<COMPILE_LANG_AND_ID:CXX,MSVC>")
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target_compile_options(tutorial_compiler_flags INTERFACE
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"$<${gcc_like_cxx}:$<BUILD_INTERFACE:-Wall;-Wextra;-Wshadow;-Wformat=2;-Wunused>>"
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"$<${msvc_cxx}:$<BUILD_INTERFACE:-W3>>"
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)
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# set the version number
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set(Tutorial_VERSION_MAJOR 1)
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@@ -19,6 +19,7 @@ if(USE_MYMATH)
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# first we add the executable that generates the table
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add_executable(MakeTable MakeTable.cxx)
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target_link_libraries(MakeTable tutorial_compiler_flags)
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# add the command to generate the source code
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add_custom_command(
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@@ -42,14 +43,17 @@ if(USE_MYMATH)
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POSITION_INDEPENDENT_CODE ${BUILD_SHARED_LIBS}
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)
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target_compile_definitions(SqrtLibrary PRIVATE
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"$<$<BOOL:${HAVE_LOG}>:HAVE_LOG>"
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"$<$<BOOL:${HAVE_EXP}>:HAVE_EXP>"
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)
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target_link_libraries(SqrtLibrary PUBLIC tutorial_compiler_flags)
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target_compile_definitions(MathFunctions PRIVATE "USE_MYMATH")
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if(HAVE_LOG AND HAVE_EXP)
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target_compile_definitions(SqrtLibrary
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PRIVATE "HAVE_LOG" "HAVE_EXP")
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endif()
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target_link_libraries(MathFunctions PRIVATE SqrtLibrary)
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endif()
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target_compile_definitions(MathFunctions PRIVATE "$<$<BOOL:${USE_MYMATH}>:USE_MYMATH>")
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target_link_libraries(MathFunctions PUBLIC tutorial_compiler_flags)
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# define the symbol stating we are using the declspec(dllexport) when
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#building on windows
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@@ -598,27 +598,47 @@ expressions are the 0 and 1 expressions. A ``$<0:...>`` results in the empty
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string, and ``<1:...>`` results in the content of "...". They can also be
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nested.
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For example:
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A common usage of generator expressions is to conditionally add compiler
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flags, such as those as language levels or warnings. A nice pattern is
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to associate this information to an ``INTERFACE`` target allowing this
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information to propagate. Lets start by constructing an ``INTERFACE``
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target and specifying the required C++ standard level of ``11`` instead
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of using ``CMAKE_CXX_STANDARD``.
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.. code-block:: cmake
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So the following code:
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if(HAVE_LOG AND HAVE_EXP)
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target_compile_definitions(SqrtLibrary
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PRIVATE "HAVE_LOG" "HAVE_EXP")
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endif()
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.. literalinclude:: Step10/CMakeLists.txt
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:language: cmake
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:start-after: project(Tutorial)
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:end-before: # Set the version number
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Can be rewritten with generator expressions:
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Would be replaced with:
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.. code-block:: cmake
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.. literalinclude:: Step11/CMakeLists.txt
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:language: cmake
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:start-after: project(Tutorial)
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:end-before: # add compiler warning flags just when building this project via
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target_compile_definitions(SqrtLibrary PRIVATE
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"$<$<BOOL:${HAVE_LOG}>:HAVE_LOG>"
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"$<$<BOOL:${HAVE_EXP}>:HAVE_EXP>"
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)
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Note that ``${HAVE_LOG}`` is evaluated at CMake configure time while
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``$<$<BOOL:${HAVE_LOG}>:HAVE_LOG>`` is evaluated at build system generation
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time.
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Next we add the desired compiler warning flags that we want for our
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project. As warning flags vary based on the compiler we use
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the ``COMPILE_LANG_AND_ID`` generator expression to control which
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flags to apply given a language and a set of compiler ids as seen
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below:
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.. literalinclude:: Step11/CMakeLists.txt
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:language: cmake
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:start-after: # the BUILD_INTERFACE genex
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:end-before: # set the version number
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Looking at this we see that the warning flags are encapsulated inside a
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``BUILD_INTERFACE`` condition. This is done so that consumers of our installed
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project will not inherit our warning flags.
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**Exercise**: Modify ``MathFunctions/CMakeLists.txt`` so that
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all targets have a ``target_link_libraries()`` call to ``tutorial_compiler_flags``.
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Adding Export Configuration (Step 11)
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=====================================
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