Allow to use Callables as setters/getters

[KoBeWi]

Describe the project you are working on

A game using GDScript that I'm going to eventually port to Godot 4.0.

Describe the problem or limitation you are having in your project

There's this new setter syntax:

var a:
  set(v):
    v = something

The problem is that it gets messy with lots of variables with setters, especially if the setters are long.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

We should be able to move the setter/getter body somewhere else. So instead of setter body, we could provide a Callable that gets called as the setter. This would also make auto-converting legacy code much easier.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

var a:
  set(v): my_setter
  get: my_getter

func my_setter(v):
  etc.

Or a shorter version:

var a: set(v): my_setter, get: my_getter

(although that's reminiscent of the old setget, which wasn't very pretty)

If this enhancement will not be used often, can it be worked around with a few lines of script?

No. Trying to call a custom method from withing setter/getter body results in infinite recursion and crash without message.

Is there a reason why this should be core and not an add-on in the asset library?

GDScript is core™

[dalexeev]

var a:
  set(v): my_setter
  get: my_getter

What function does v serve in your example? You can already use this:

var a:
  set(v): my_setter(v)
  get: return my_getter()

IMO this is already short enough, but we can add the following syntax:

var a:
  set = my_setter
  get = my_getter

or

var a: set = my_setter, get = my_getter

Note that an equal sign is used instead of a colon. I think this is more logical and consistent with the rest of the syntax.

[KoBeWi]

What function does v serve in your example? You can already use this:

my_setter(v) won't work (godotengine/godot#52757). The v is not needed, but I included it, so the syntax doesn't need to change.

Well, but if we were to introduce new syntax, your proposed one is better.

[dalexeev]

my_setter(v) won't work (godotengine/godot#52757).

This is incorrect code, and it shouldn't work (but of course it shouldn't crash the engine). It should be like this:

var my_var:
    get: return get_my_var()
    set(value): set_my_var(value)

var _my_var

func get_my_var():
    return _my_var

func set_my_var(value):
    _my_var = value

By design, access to my_var should call get and set everywhere except within get and set. This is convenient for its consistency.

Do I understand correctly what you suggest that in the functions get_my_var and set_my_var, accessing my_var does not cause infinite recursion (if var my_var: get = get_my_var, set = set_my_var)? And so there was no need for _my_var? This can be convenient, but it creates additional non-obviousness.

[KoBeWi]

Looking at it again, my proposal has the same problem as the code that causes infinite recursion .-.

So I guess

Do I understand correctly what you suggest that in the functions get_my_var and set_my_var, accessing my_var does not cause infinite recursion (if var my_var: get = get_my_var, set = set_my_var)?

This has to be true.

All these problems are caused by the fact that you can no longer change a property without triggering setter/getter. It's problematic.

[vnen]

This syntax already exists:

var my_prop:
    get = get_my_prop, set = set_my_prop

[KoBeWi]

🙃