Private by Convention

Part of the Object Oriented Programming section of Coddy's GDScript journey. Lesson 13 of 65.

GDScript has no private keyword: every property and method of an object can be reached from other scripts. Godot's convention is a leading underscore. _coins and _is_valid() below are meant for the class's own code only:

# wallet.gd
class_name Wallet
extends RefCounted

var _coins: int = 0

func add(amount: int) -> void:
	if _is_valid(amount):
		_coins += amount

func spend(amount: int) -> bool:
	if not _is_valid(amount) or amount > _coins:
		return false
	_coins -= amount
	return true

func get_coins() -> int:
	return _coins

func _is_valid(amount: int) -> bool:
	return amount > 0

Other scripts use the public methods, and those check every change: spend() refuses to take more coins than the wallet holds, so the number of coins never goes below zero.

var wallet := Wallet.new()
wallet.add(50)
wallet.add(-20)
print(wallet.spend(80)) # false
print(wallet.get_coins()) # 50

The underscore is a promise, not a lock: wallet._coins = -999 runs without any error. Keeping the promise is up to whoever writes the other scripts, so do not read or change underscored members from outside their class.

You already know two underscore names from Godot itself: _ready() and _init() are called by the engine, not by your own code.

Challenge

Easy

Complete the class User in user.gd. It keeps its password in a private property, _password, and only its own code touches it.

The constructor stores the starting password
check_password(attempt) returns whether attempt matches the password
_is_strong(candidate), a private helper, returns whether candidate has at least 6 characters
change_password(old_password, new_password) changes the password and returns true only when old_password is correct and new_password is strong. Otherwise it changes nothing and returns false

The supplied code reads the starting password, how many commands follow, and the commands check PASSWORD and change OLD NEW. For the password godot4 and the commands change godot4 abc, change wrong longenough and check godot4 it prints:

Password not changed
Password not changed
Access granted

Your code goes in user.gd. main.gd holds the supplied input/output code and cannot be edited.

Try it yourself

extends Node

func _ready():
	# Supplied input/output code: keep it as it is
	var user := User.new(OS.read_string_from_stdin())
	var count := int(OS.read_string_from_stdin())
	for i in count:
		var parts := OS.read_string_from_stdin().split(" ")
		if parts[0] == "check":
			print("Access granted" if user.check_password(parts[1]) else "Access denied")
		elif user.change_password(parts[1], parts[2]):
			print("Password changed")
		else:
			print("Password not changed")