Typed arrays aren't working with +=

[EamonnMR]

Godot version

v4.0.rc1.official [8843d9a]

System information

Lubuntu

Issue description

You can't use + or += to mutate typed arrays.

It seems to be not correctly getting the type information from the second operand.

An erudite poster on the discord puts it differently:

it's more like operator + doesn't retain Array typing
the syntax for Array Concatenation via operators, but the idea gets across i think

The error you see is:
Trying to assign an array of type "Array" to a variable of type "Array[int]".

Steps to reproduce

	var Alice: Array[int] = [1,2,3]
	var Bob: Array[int] = [4,5,6]
	Alice += Bob

This will crash with the above error message.

Minimal reproduction project

plus_syntax_broken_demo_project.zip

[Haledire]

Specifically - the operator + as the docs describe returns a Variant Array

when you do (in this example) Alice + Bob, the returned array loses the typing - going from Array[int] to just Array

append_array() works to concatenate the same typed arrays, but the operator itself can't seem to maintain the typing

Alice = Alice + Bob   # fails
Alice += Bob          # fails
Alice.append_array(Bob)  #succeeds

[esarver]

I see the same issue when initializing arrays like:

var membervar: Array[ClassDefinedElseWhere] = Array()

It seems like this is a more general issue.

[YuriSizov]

@esarver This is not the same issue. You are trying to assign an untyped array to a typed property, which is not possible due to ambiguous behavior. You need to use the assign method of the array if you want to convert your value to the typed array.

If you only want to initialize your property, an array literal should work, [].