C++ usage guidelines

Rationale

C++17. While modern C++ brings a lot of opportunities to write faster, more readable code, we chose to restrict our usage of C++ to a subset for a few reasons:

• It makes it easier to review code in online editors. This is because engine contributors don’t always have access to a full-featured IDE while reviewing code.
• It makes the code easier to grasp for beginner contributors (who may not be professional C++ programmers). Godot’s codebase is known to be easy to learn from, and we’d like to keep it that way. To get your pull request merged, it needs to follow the C++ usage guidelines outlined here. Of course, you can use features not allowed here in your own C++ modules or GDNative scripts. Note Prior to Godot 4.0, the C++ standard used throughout the codebase was C++03, with a handful of C++14 extensions. If you are contributing a pull request to the 3.x branch rather than master, your code can’t use C++17 features. Instead, your code must be able to be built with a C++14 compiler. Best practices for engine contributors. See also Code style guidelines for formatting guidelines.

  Disallowed features

  Any feature not listed below is allowed. Using features like constexpr variables and nullptr is encouraged when possible. Still, try to keep your use of modern C++ features conservative. Their use needs to serve a real purpose, such as improving code readability or performance.

  Standard Template Library

  STL as Godot provides its own data types (among other things). See Why does Godot not use STL (Standard Template Library)? for more information. not use std::string, std::vector and the like. Instead, use Godot’s datatypes as described below:
• String instead of std::string.
• Vector instead of std::vector. In some cases, LocalVector can be used as an alternative (ask core developers first).
• Array instead of std::array. Note Godot also has a List datatype (which is a linked list). While List is already used in the codebase, it typically performs worse than other datatypes like Vector and Array. Therefore, List should be avoided in new code unless necessary.

  auto keyword

  auto keyword for type inference. While it can avoid repetition, it can also lead to confusing code:

  // Not so confusing...auto button = memnew(Button);// ...but what about this?auto result = EditorNode::get_singleton()->get_complex_result();

  Keep in mind hover documentation often isn’t readily available for pull request reviewers. Most of the time, reviewers will use GitHub’s online viewer to review pull requests. auto instead of allowing it on a case-by-case basis to avoid having to decide on difficult edge cases. Thank you for your understanding.

  Lambdas

  Lambdas should be used conservatively when they make code effectively faster or simpler, and do not impede readability. Please ask before using lambdas in a pull request.

  #pragma once directive

  #ifdef-based include guards instead of #pragma once in new files. See also Header includes for guidelines on sorting includes in C++ and Objective-C files.