jayyi3 / cpp-module Goto Github PK

C++ 20 introduces modules, which allow compilers to use "semantic imports" instead of the old text inclusion model.

Modules allow shared declarations and definitions across translation units. A module is a set of source files that are compiled independently and only once. It has several advantages over header files:

• Reduced compilation time.
• Hide visibility of internal implementations like macros, preprocessor directives, and non-exported names.
• Modules can be imported in any order without concern for dependencies between headers.

There is a simple example inside the examples folder, and a script containing the commands to run it.

Here is an article that compares header files, header units, modules and precompiled header. Support for modules of different compiler vendors can be found here (the Modules row in the 'C++20 core language features' table). This video gives a great introduction to modules.

Modules can be structured into several ways:

• Primary Module Interface Unit

  Both module interface and implementation goes into a single file(like a header-only library).

  // File: my_module.cpp
  export module my_module;
  
  export char const* my_func() {
    return "Hello Modules!";
  }

• Module Implementation Unit

  Module interface and implementation goes into a separate file(similar to header files and source files).

  // File: my_module.cpp
  export module my_module;
  
  export char const* my_func();
  
  // File: my_module_impl.cpp
  module my_module;
  
  char const* my_func() {
    return "Hello Modules!";
  }

• Module Interface Partitions

  This is used for structuring the internal of a module

  // File: my_module.cpp
  export module m;
  
  export import :p1;
  export import :p2;
  
  // File: my_module_p1.cpp
  export module m:p1;
  export void p1_func() {}
  
  // File: my_module_p2.cpp
  export module m:p2;
  export void p2_func() {}