Accept inheriting class when parent class is used in Array type hinting

[tyson-nw]

Describe the project you are working on:
I have a generic class called Token with two child classes, AntagonistToken and ProtagonistToken. I would like to be able to pass an array of a mix of tokens in an array to a function with Type hinting

Describe the problem or limitation you are having in your project:
Currently type hinting of Array content requires the passed objects to specifically be of the class listed. You cannot pass an aray of objects of a child classes to the function.

Show a mock up screenshots/video or a flow diagram explaining how your proposal will work:

You would be allowed to pass a mix of objects that all have the same base class to a function that is type hinted.

func _ready()
    function_name(get_children())

func function_name(objects : Array[Token])
   for object in objects:
      object.do_token_func()
      if object is AntagonistToken:
         object._do_antagonist_func()
      elif object is ProtagonistToken:
         object._do_protagonist_func()

[sockeye-d]

This is actually quite an interesting problem and it's not super easy to solve. Since the type is stored in the object and not in the variable, you could consider a situation like this:

var array1: Array[Child] = ...
var array2: Array[Parent] = array1
# the object in array2 still only accepts Child types and "smaller"
# but array2 itself suggests we can add parents to it
array2.append(Parent.new())
# static code analysis says this is okay,
# but you get a runtime error from this

More information: https://en.m.wikipedia.org/wiki/Covariance_and_contravariance_(computer_science)