README.md

Modules

💡 Module is a way to organize, encapsulate, and isolate your code.

Advantages:

• Better compilation times

  Modules are processed only once. Compare this with M headers which are included in N translation units. The combinatorial explosion means, that the header has to be parsed M * N times.

• No need of header files

  Separation into interface and implementation files is possible but it is obsolete.

• No need for include guard

• Preprocessor usage elimination

• No need to invent unique names

  Same names in multiple modules will not clash.

• The order of import statements will not matter

// hello.cpp/.cppm/.mpp
export module hello;

namespace hello {

auto GetWelcomeMessage() {
  return "Welcome to C++20!";
}

export auto SayWelcome() {
  return GetWelcomeMessage();
}

} // namespace hello

// main.cpp/.cppm/.mpp
import hello;

import <iostream>;

int main() {
  cout << hello::SayWelcome();
}

📎 You can import header files, e.g.

import <iostream>;

• Implicitely turns the iostream header into module
• Improves build throughput, as iostream will then processed only once

📋 Structure

Module (top to bottom)
module;
preprocessor derictives only, e.g #include <cassert>
export module name;
import ...;
...
module : private;
...

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