Module Partitions vs Submodules

Module partitions and submodules are two techniques in C++20 that help organize and manage code within modules. They serve different purposes and have distinct characteristics.

Module Partitions

Module partitions allow you to split a single module into multiple parts, which helps in managing large modules.

Partitions are internal to the module and are used to organize the implementation details. Here’s an example:

1// Math.cppm
2export module Math;
3
4export import :Algebra;
5export import :Geometry;
6
7export int add(int a, int b);

1// Math:Algebra.cppm
2module Math:Algebra;
3
4export int multiply(int a, int b) {
5  return a * b;
6}

1// Math:Geometry.cppm
2module Math:Geometry;
3
4export double calculateCircleArea(double radius) {
5  return 3.14 * radius * radius;
6}

Characteristics of Module Partitions

• Internal Structure: Partitions are used to divide the internal structure of a single module.
• Visibility: Partitions are not visible outside the module. They are used to manage the implementation details within the module.
• Import Syntax: Partitions are imported using the import :partitionName syntax within the module.

Submodules

Submodules, on the other hand, are independent modules that can form a hierarchy.

They allow you to create modular and reusable code components that can be imported separately or as a group. Here’s an example:

1// Math.Algebra.cppm
2export module Math.Algebra;
3
4export int multiply(int a, int b) {
5  return a * b;
6}

1// Math.Geometry.cppm
2export module Math.Geometry;
3
4export double calculateCircleArea(double radius) {
5  return 3.14 * radius * radius;
6}

1// Math.cppm
2export module Math;
3
4export import Math.Algebra;
5export import Math.Geometry;

Characteristics of Submodules

• Hierarchy: Submodules create a hierarchical structure, allowing for independent and reusable code components.
• Visibility: Submodules are visible outside the parent module and can be imported individually or as part of the parent module.
• Import Syntax: Submodules are imported using the import moduleName.submoduleName syntax.

Key Differences

• Purpose: Partitions are for organizing the internal structure of a single module, while submodules create a hierarchy of independent modules.
• Visibility: Partitions are not visible outside the module, whereas submodules are.
• Usage: Partitions use the :partitionName syntax and are internal, while submodules use the moduleName.submoduleName syntax and are external.

Summary

Module partitions and submodules are both useful tools in C++20 for organizing code within modules. Partitions help manage the internal structure of a module, while submodules create a hierarchy of independent modules that can be imported separately or together.