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C++ usage guidelines

Rationale

Since Redot 4.0, the C++ standard used throughout the codebase is a subset of 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). Redot'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 GDExtensions.

Note

Prior to Redot 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.

The guidelines below don't apply to third-party dependencies, although we generally favor small libraries instead of larger solutions. See also Best practices for engine contributors.

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

We don't allow using the STL as Redot provides its own data types (among other things). See Why does Redot not use STL (Standard Template Library)? for more information.

This means that pull requests should not use std::string, std::vector and the like. Instead, use Redot's datatypes as described below:

Use String instead of std::string.
Use Vector instead of std::vector. In some cases, LocalVector can be used as an alternative (ask core developers first).
Use Array instead of std::array.

Note

Redot 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

Please don't use the 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.

We chose to forbid 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

To follow the existing style, please use standard #ifdef-based include guards instead of #pragma once in new files.