Godot: yield with function doesn't work

[grevius5]

Godot version:
3.2 beta 3
OS/device including version:
Linux Manjaro
Issue description:
In the documentation for the yield you can see that:

You can also use yield to wait for a function to finish:

func _ready():
    yield(do_something(), "completed")
    yield(do_something_else(), "completed")
    print("All functions are done!")

func do_something():
    print("Something is done!")

func do_something_else():
    print("Something else is done!")

but if you try to yield a function you will get that error:

First argument of yield() not of type object.

Steps to reproduce:
yield(print("ok"), "completed")

[dalexeev]

@grevius5 See the documentation.

GDScriptFunctionState yield( Object object=null, String signal="" )

print("ok") returns null. This is not an object.
To wait for a function to complete, you should use something like the following:

extends Node

func f():
    print('f 1')
    yield(get_tree().create_timer(3), 'timeout')
    print('f 2')

func _ready():
    print('_ready 1')
    yield(f(), 'completed')
    print('_ready 2')

See also #31494.

[grevius5]

@dalexeev so is wrong the example in the documentation because it calls simple functions with only a print

[dalexeev]

@grevius5 I tried to find the phrase on the Internet, but did not find an exact match. Could you provide a link?

Official documentation:

[grevius5]

I have this in my 3.2 beta 3 godot internal documentation

[dalexeev]

Indeed, this example (apparently incorrect) was added recently. #33872
@zaksnet @akien-mga

[zaksnet]

Hello guys,
It seems that in order to yield, the function you are yielding also needs to inherit from GDScriptFunctionState. So the documentation should be changed to :

func _ready():
    yield(do_something(), "completed")
    yield(do_something_else(), "completed")
    print("All functions are done!")

func do_something():
    yield(get_tree(), "idle_frame")
    print("Something is done!")

func do_something_else():
    yield(get_tree(), "idle_frame")
    print("Something else is done!")

Notice the yield(get_tree(), "idle_frame") in do_something functions.
Of course yield(get_tree(), "idle_frame") can be anything but this seems reasonable because it will only yield for an idle frame. Sorry i though this was optional and as a result documented it as optional.

If you are planning on calling the same function within a loop, you should consider using [code]yield(get_tree(), "idle_frame")[/code] also. <--- From the docs

[dalexeev]

_Ready():

func _ready():

:smile:

[zaksnet]

_Ready():

func _ready():

😄

Been losing my mind lately going c# to GDScript >.<

[dalexeev]

func _Ready():

func _ready():

GDScript is a case-sensitive programming language!
Do not rush like that. :smile: :smile: :smile:

[Xrayez]

await should solve most of these incorrect usages in the future hopefully: #32034, #33224 (meaning if you do pass null to await, it should handle that without errors).

I've also written some docs on this in godotengine/godot-docs#2644.

[dalexeev]

Fixed in #34280.