Gdscript strange behaviour (bug?)

sephen

I've noticed some strange behaviour in gdscript.

when you declare variables

var value = [0, 0, 0, 0, 0]
var values = []

and append one to the other values.append(value)

and then change something in the first value[1] = 1

If you would then print the results print(value, values)

It also changes the previous appended value prints: [0, 1, 0, 0, 0][[0, 1, 0, 0, 0]]

expected behaviour prints: [0, 1, 0, 0, 0][[0, 0, 0, 0, 0]]

TwistedTwigleg

Welcome to the forums @sephen!

This is not a bug, arrays in Godot are passed by reference instead of by value. Unlike most types in Godot, when you change a value in an array all copies of that array will be changed as well. If you want to make a copy of the array, you will need to use the duplicate function to duplicate the array rather than get a reference:

var value = [0, 0, 0, 0, 0]
var values = []

# Duplicate so we have a unique array
values.append(value.duplicate())
values.append(value)

# change the unique array
values[0][1] = 2
# change the shared reference array
value[1] = 4
values[1][0] = 8

print (value, values)

sephen

Thanks! @TwistedTwigleg !

That explains a lot... Lost the good part of a day over this :)