GDScript Classes: class_name, _init() and new()

Every GDScript file is a class. Its member variables are the fields, its functions are the methods, and extends names the class it builds on. A script can also define classes inside it, which is how this example runs in one file:

extends Node

class Enemy:
	var kind: String
	var hp: int

	func _init(enemy_kind: String, start_hp: int = 10):
		kind = enemy_kind
		hp = start_hp

	func take_damage(amount: int) -> void:
		hp = max(hp - amount, 0)

	func is_alive() -> bool:
		return hp > 0

func _ready():
	var slime := Enemy.new("slime")
	var golem := Enemy.new("golem", 50)
	slime.take_damage(12)
	golem.take_damage(12)
	print(slime.kind, " alive: ", slime.is_alive())
	print(golem.kind, " hp: ", golem.hp)

slime alive: false
golem hp: 38

• Enemy.new(...) creates an instance and calls _init() with the arguments.
• Each instance has its own kind and hp.
• Inside a method, members are used by name. self.hp means the same and is only needed when a local variable has the same name.

class_name: Naming a Script

In a real project you put a class in its own file and name it with class_name:

# enemy.gd
class_name Enemy
extends CharacterBody2D

@export var max_hp := 10
var hp: int

func _ready():
	hp = max_hp

func take_damage(amount: int) -> void:
	hp -= amount
	if hp <= 0:
		queue_free()

Now every script can use Enemy as a type: var target: Enemy, if body is Enemy:, and Enemy shows up in the Create Node dialog. Without class_name, you would load the script by path: const Enemy = preload("res://enemy.gd").

The two lines can also be written as one: class_name Enemy extends CharacterBody2D.

Nodes and Scenes Are Classes Too

A script that extends a node type is instantiated by Godot when it loads the scene, so you rarely call new() on it. You spawn a whole scene instead:

const EnemyScene = preload("res://enemy.tscn")

func spawn_enemy(at: Vector2) -> void:
	var enemy: Enemy = EnemyScene.instantiate()
	enemy.position = at
	add_child(enemy)

Enemy.new() would create the bare script node with none of the scene's children, such as its sprite and collision shape. Use new() for plain data classes and nodes you build entirely in code.

Because scenes create nodes by calling _init() with no arguments, a node script's _init() should not require parameters.

Printing an Object

print() on an object shows its class and id. Define _to_string() to choose the text:

extends Node

class Item:
	var item_name: String
	var price: int

	func _init(n: String, p: int):
		item_name = n
		price = p

	func _to_string() -> String:
		return "%s (%d gold)" % [item_name, price]

func _ready():
	var sword := Item.new("Sword", 50)
	print(sword)
	print([sword, Item.new("Shield", 30)])

Sword (50 gold)
[Sword (50 gold), Shield (30 gold)]

Which Class to Extend

A script with no extends line extends RefCounted. See resources for data classes the editor can show.

Checking an Object's Class

extends Node

class Coin:
	var value := 1

func _ready():
	var coin := Coin.new()
	print(coin is Coin)
	print(coin is RefCounted)
	print(self is Node, " ", get_class())
	print(coin.get("value"), " ", "value" in coin)

true
true
true Node
1 true

is works with engine classes and your own classes. get_class() returns the engine class name, which is the built-in base, not your script's name. in and get() look up a property by its name.

Classes build on each other with inheritance, and properties can run code when read or written with setters and getters.