c++23 modules example

CMakeLists.txt

cmake_minimum_required(VERSION 3.30)

# Set experimental flag to enable `import std` support from CMake.
# This must be enabled before C++ language support.
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
  # This specific value changes as experimental support evolves. See
  # `Help/dev/experimental.rst` in the CMake source corresponding to
  # your CMake build for the exact value to use.
  "0e5b6991-d74f-4b3d-a41c-cf096e0b2508")
project(std_module_example CXX)

# Tell CMake that we explicitly want `import std`. This will initialize the
# property on all targets declared after this to 1
set(CMAKE_CXX_MODULE_STD 1)

set(CMAKE_EXPORT_COMPILE_COMMANDS ON)

# Turning off extensions avoids an issue with the clang 16 compiler
# clang 17 and greater can avoid this setting
set(CMAKE_CXX_EXTENSIONS ON)
# Set the version of C++ for the project
set(CMAKE_CXX_STANDARD 23)
# Create a library
add_library(foo STATIC)
# Add the module file to the library
target_sources(foo PUBLIC FILE_SET CXX_MODULES FILES foo_interface.cpp)
target_sources(foo PUBLIC foo_impl.cpp)
target_compile_features(foo INTERFACE cxx_std_23)
# Create an executable
add_executable(hello)

target_sources(hello PRIVATE main.cpp)
# Link to the library foo
target_link_libraries(hello PRIVATE foo)

foo_impl.cpp

//module;
//#include <whatever>
module foo;
import std;

void f() { std::cout << "f()\n"; }

foo::foo() = default;
foo::~foo() = default;
void foo::helloworld() { std::cout << "hello world\n"; }

foo_interface.cpp

export module foo;

export class foo {
public:
  foo();
  ~foo();
  void helloworld();
  void other();
};

export void f();
export void g();

main.cpp

import foo;

int main()
{
  foo fo;
  fo.helloworld();
  f();
  return 0;
}