C++20 Modules tryout

CMakeLists.txt

cmake_minimum_required(VERSION 3.19) # Lower versions should also be supported
project(cpp20-modules)

# Add target to build iostream module
add_custom_target(std_modules ALL
    COMMAND ${CMAKE_COMMAND} -E echo "Building standard library modules"
    COMMAND g++ -fmodules-ts -std=c++20 -c -x c++-system-header iostream
    WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
)

# Function to set up modules in GCC
function (prepare_for_module TGT)
    target_compile_options(${TGT} PUBLIC -fmodules-ts)
    set_property(TARGET ${TGT} PROPERTY CXX_STANDARD 20)
    set_property(TARGET ${TGT} PROPERTY CXX_EXTENSIONS OFF)
    add_dependencies(${TGT} std_modules)
endfunction()

# Program name and sources
set (TARGET prog)
set (SOURCES main.cpp)
set (MODULES mod.cpp)

# Setup program modules object library
set (MODULE_TARGET prog-modules)
add_library(${MODULE_TARGET} OBJECT ${MODULES})
prepare_for_module(${MODULE_TARGET})

# Setup executable
add_executable(${TARGET} ${SOURCES})
prepare_for_module(${TARGET})

# Add modules to application using object library
target_link_libraries(${TARGET} PRIVATE ${MODULE_TARGET})

main.cpp

import math;
import <iostream>;

int main (int, char *argv[]) {
	std::cout << add(2000, 20) << '\n';
  return 0;
}

mod.cpp

export module math;

export int add(int fir, int sec){
    return fir + sec;
} 

run_command

cmake . -Bout/ && make -C out/ && ./out/prog