Defer in GDScript

In GDScript, we don’t have a direct equivalent to the defer keyword. However, we can achieve similar functionality using GDScript’s _exit_tree() method or by using a custom defer implementation. For this example, we’ll create a custom defer mechanism.

Our program will demonstrate how to create a file, write to it, and ensure it’s closed properly:

extends Node

var _deferred_calls = []

func _ready():
    var f = create_file("/tmp/defer.txt")
    defer(funcref(self, "close_file"), [f])
    write_file(f)

func create_file(path):
    print("creating")
    var file = File.new()
    var error = file.open(path, File.WRITE)
    if error != OK:
        push_error("Failed to create file")
    return file

func write_file(file):
    print("writing")
    file.store_line("data")

func close_file(file):
    print("closing")
    file.close()

func defer(func_ref, args = []):
    _deferred_calls.push_back([func_ref, args])

func _exit_tree():
    for call in _deferred_calls:
        var func_ref = call[0]
        var args = call[1]
        func_ref.call_funcv(args)

This script does the following:

1. We define a custom defer function that stores function references and their arguments to be called later.

2. In the _ready() function (which is called when the node enters the scene tree), we create a file, defer its closing, and write to it.

3. The create_file() function creates a new file and returns a File object.

4. The write_file() function writes data to the file.

5. The close_file() function closes the file.

6. In the _exit_tree() function (which is called when the node is about to be removed from the scene tree), we execute all deferred function calls.

To run this script, you would need to attach it to a Node in your Godot scene. When the scene is loaded and then unloaded, you should see the following output:

creating
writing
closing

This approach ensures that the file is closed even if an error occurs during writing. It’s important to note that in a real-world scenario, you should also handle potential errors when closing the file.

While this implementation isn’t as clean as Go’s built-in defer keyword, it provides similar functionality in GDScript. Remember to always properly manage resources like files, even when using deferred execution patterns.