Applying object-oriented principles in Godot

The engine offers two main ways to create reusable objects: scripts and scenes. Neither of these technically define classes under the hood.

Still, many best practices using Godot involve applying object-oriented programming principles to the scripts and scenes that compose your game. That is why it’s useful to understand how we can think of them as classes.

This guide briefly explains how scripts and scenes work in the engine’s core to help you understand how they work under the hood.

How scripts work in the engine

The engine provides built-in classes like Node. You can extend those to create derived types using a script.

These scripts are not technically classes. Instead, they are resources that tell the engine a sequence of initializations to perform on one of the engine’s built-in classes.

Godot’s internal classes have methods that register a class’s data with a ClassDB. This database provides runtime access to class information. ClassDB contains information about classes like:

• Properties.

• Methods.

• Constants.

• Signals.

This ClassDB is what objects check against when performing an operation like accessing a property or calling a method. It checks the database’s records and the object’s base types’ records to see if the object supports the operation.

Attaching a Script to your object extends the methods, properties, and signals available from the ClassDB.

Note

Even scripts that don’t use the extends keyword implicitly inherit from the engine’s base Reference class. As a result, you can instantiate scripts without the extends keyword from code. Since they extend Reference though, you cannot attach them to a Node.

Scenes

The behavior of scenes has many similarities to classes, so it can make sense to think of a scene as a class. Scenes are reusable, instantiable, and inheritable groups of nodes. Creating a scene is similar to having a script that creates nodes and adds them as children using add_child().

We often pair a scene with a scripted root node that makes use of the scene’s nodes. As such, the scene is often an extension of the script’s declarative code.

The content of a scene helps to define:

• What nodes are available to the script

• How they are organized

• How they are initialized

• What signal connections they have with each other

Why is any of this important to scene organization? Because instances of scenes are objects. As a result, many object-oriented principles that apply to written code also apply to scenes: single responsibility, encapsulation, and others.

The scene is always an extension of the script attached to its root node, so you can interpret it as part of a class.

Most of the techniques explained in this best practices series build on this point.