How to duplicate a variable (like an Array) in GDscript

Question

I want to know how I can pass values NOT by reference, but by value. When I write:

var array1 = [1,2,3,4,77,788]
var array2 = array1
array2.push_back(1)
print(array1) #print': 1,2,3,4,77,788,1

They are passed by reference.
because array1 and array2 two "point" to the same data.
How can I duplicate them. I'm searching for something like:

array2 = array1.cloned()

For arrays specific I already know some work arounds but how do I do it with custom objects?

Comments

There are somewhat related issues on github:
(about array cloning) https://github.com/godotengine/godot/issues/3697
(about duplicate) https://github.com/godotengine/godot/issues/3393

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thank you these threads are both interesting!

Answer 1

Since all objects that you create via script are Nodes, you can use

Node duplicate( bool use_instancing=false ) const

It will return a reference to a copy of the Node you are duplicating, so you can just store it on a var.

~EDIT~
As for the data structures, if there is no copy method embedded on it, I think you'd have to create a function yourself. Most of the basics Data Structures have a very straightforward copy mechanism, anyway.

Comments

Thank you!
Are they really always nodes also if I don't write: extends Node ?
This is exactly what I was searching for.

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I'm not too sure about this, but I think that when you are creating a script, you have to extend it from somewhere, UNLESS it is a "tool" tagged script (something you'll use on the Editor).

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you don't need to use the extends Anything line (I already tried it without). The question is if it extends something as default.

Answer 2

Try this.

var array2 = [] + array1

Comments

Good method. I already was aware of another less comfortable way to do it with arrays. So this can be quiet useful when I need it next time.

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Anyone know a solution for dictionaries? As "+" is invalid for dicts for no good reason I can see :/

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poster by Bojidar:

With str2var(var2str(...)), you can effectively clone any object, at the high cost of speed.

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Wow... That's handy.

Answer 3

This answer is mostly compiled from the issues @kubecz3k linked.

With str2var(var2str(...)), you can effectively clone any object, at the high cost of speed.

Unfortunately, the following method doesn't actually work... It would create the array in Copy-on-Write mode in Godot 1.x/2.x, which is rather useless for cloning. Better use @volzhs answer, or the str2var method.
The Array constructor accept a array to clone, so you can just do Array(my_arr). There are similar use for the Dictionary and typed array constructors as well. Unfortunately, this doesn't work for everything (like custom object classes).

Nodes have a .duplicate method, but it is already covered in another answer.

Comments

For some reason, the Array constructor doesn't work for me. It has the same effect as doing newArr = oldArr.

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Actually, it seems like it was an unintended feature in Godot 2.x. It would actually create an array in Copy-on-Write mode, and it would be fixed in 3.0. So, for now, better clone it by yourself or use @volzhs method.

Answer 4

New methods in array and dictionary can be used for duplication.

For array
https://docs.godotengine.org/en/3.1/classes/class_array.html#class-array-method-duplicate

For dictionary
https://docs.godotengine.org/en/3.1/classes/class_dictionary.html#class-dictionary-method-duplicate

var first_array = [
                    {10 : [10, 20, 30, 40]},
                    {20 : [10, 20, 50, 80]}]
var second_array = first_array.duplicate(true)
second_array.append({30 : [10, 30, 40, 70]})
print(first_array)
print(second_array)

var first_dict = { 10: [10, 20, 30, 40],
                   20: [10, 20, 50, 80]}
var second_dict = first_dict.duplicate(true)
second_dict[30] = [10, 30, 40, 70]
print(first_dict)
print(second_dict)

Comments

Didn't you read the selected answer?

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I read the selected answer but did not know how to use it. So I created another answer instead of comment.

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Fair enough.