Inconsistency in boolean validation of [Freed Object]

[h0lley]

Godot version

v4.0.alpha5.official [d7d528c]

System information

Ubuntu

Issue description

I'm aware we ought to use is_instance_valid() to validate an Object.
However in Godot 4 things may be a little different since comparison with null is now possible.
While [Freed Object] == null and not [Freed Object] was false in Godot 3, it is now true in 4.

However, [Freed Object] still validates to true in an if, while null validates to false.
This now results in very strange behavior:

var lele = Node.new()
lele.free()

if lele and not lele:
    print("this prints")

or:

if lele == null:
    print(lele, " is null")

if lele:
    print(lele, " is true")

if not null:
    print("null is false")

[Freed Object] is null
[Freed Object] is true
null is false

Many new users try comparison with null first before learning about is_instance_valid() (why this doesn't work in Godot 3 is a very common question). Since this yields the expected result now, they'll likely stick to it and never learn about is_instance_valid(). Treating [Freed Object] like null will however end up in users assuming if [Freed Object]: will validate to false, which it does not.

So here's the two solutions I can see (either or):

• Behavior of Godot 3 should be restored
  • Meaning [Freed Object] == null and not [Freed Object] should both be false again
• if [Freed Object]: should validate to false as well
  • Which would reduce complexity as we could actually do away with is_instance_valid()

Steps to reproduce

Run example code in a _ready function.

Minimal reproduction project

No response

[Calinou]

cc @vnen

[dalexeev]

I also wanted to report this. I hope this will be helpful.

print	3.4.2 Freed Object	3.4.2 null	4.0a5 Freed Object	4.0a5 null	Option 1	Option 2
value	[Deleted Object]	Null	[Freed Object]	null	[Freed Object]	[Freed Object]
not value	False	True	true	true	false	true
"+" if value else "-"	+	-	+	-	+	-
is_instance_valid(value)	False	False	false	false	false	false
value == null	False	True	true	true	false	true
typeof(value) == TYPE_NIL	False	True	false	true	false	true
typeof(value) == TYPE_OBJECT	True	False	true	false	true	false
value is Object	True	False	true	false	true	false
value is Node	Error	False	Error	false	???	false

Details

v3.4.2.stable.official [45eaa2d]

tool
extends EditorScript

func test(value):
    print("-----")
    print("value                         ", value)
    print("not value                     ", not value)
    print('"+" if value else "-"         ', "+" if value else "-")
    print("is_instance_valid(value)      ", is_instance_valid(value))
    print("value == null                 ", value == null)
    print("typeof(value) == TYPE_NIL     ", typeof(value) == TYPE_NIL)
    print("typeof(value) == TYPE_OBJECT  ", typeof(value) == TYPE_OBJECT)
    print("value is Object               ", value is Object)
    print("value is Node                 ", value is Node)

func _run():
    var object = ClassDB.instance("Object")
    object.free()
    test(object)

    var node = Node.new()
    node.free()
    test(node)

    test(null)

-----
value                         [Deleted Object]
not value                     False
"+" if value else "-"         +
is_instance_valid(value)      False
value == null                 False
typeof(value) == TYPE_NIL     False
typeof(value) == TYPE_OBJECT  True
value is Object               True
 res://_dev/_run.gd:14 - Left operand of 'is' was already freed.
-----
value                         [Deleted Object]
not value                     False
"+" if value else "-"         +
is_instance_valid(value)      False
value == null                 False
typeof(value) == TYPE_NIL     False
typeof(value) == TYPE_OBJECT  True
value is Object               True
 res://_dev/_run.gd:14 - Left operand of 'is' was already freed.
-----
value                         Null
not value                     True
"+" if value else "-"         -
is_instance_valid(value)      False
value == null                 True
typeof(value) == TYPE_NIL     True
typeof(value) == TYPE_OBJECT  False
value is Object               False
value is Node                 False

v4.0.alpha5.official [d7d528c]

@tool
extends EditorScript

func test(value):
    print("-----")
    print("value                         ", value)
    print("not value                     ", not value)
    print('"+" if value else "-"         ', "+" if value else "-")
    print("is_instance_valid(value)      ", is_instance_valid(value))
    print("value == null                 ", value == null)
    print("typeof(value) == TYPE_NIL     ", typeof(value) == TYPE_NIL)
    print("typeof(value) == TYPE_OBJECT  ", typeof(value) == TYPE_OBJECT)
    print("value is Object               ", value is Object)
    print("value is Node                 ", value is Node)

func _run():
    var object = ClassDB.instantiate("Object")
    object.free()
    test(object)

    var node = Node.new()
    node.free()
    test(node)

    test(null)

-----
value                         [Freed Object]
not value                     true
"+" if value else "-"         +
is_instance_valid(value)      false
value == null                 true
typeof(value) == TYPE_NIL     false
typeof(value) == TYPE_OBJECT  true
value is Object               true
  res://_dev/_run.gd:14 - Left operand of 'is' is a previously freed instance.
-----
value                         [Freed Object]
not value                     true
"+" if value else "-"         +
is_instance_valid(value)      false
value == null                 true
typeof(value) == TYPE_NIL     false
typeof(value) == TYPE_OBJECT  true
value is Object               true
  res://_dev/_run.gd:14 - Left operand of 'is' is a previously freed instance.
-----
value                         null
not value                     true
"+" if value else "-"         -
is_instance_valid(value)      false
value == null                 true
typeof(value) == TYPE_NIL     true
typeof(value) == TYPE_OBJECT  false
value is Object               false
value is Node                 false

I don't know how the is operator should behave in this case. Should inheritance be checked for freed objects?

print	Freed Object	Freed Node	null
value is Object	true	true	false
value is Node	false	true	false

It's probably not possible, but it's strange that is works for Object but doesn't work for child classes. In my understanding, is should be a safe operator.

• if [Freed Object]: should validate to false as well

I don't think this is the right solution, if [Freed Object]: and if not [Freed Object]: should not both be false (since not [Freed Object] should be false).

[h0lley]

I don't think this is the right solution, if [Freed Object]: and if not [Freed Object]: should not both be false (since not [Freed Object] should be false).

not [Freed Object] would be true as is currently the case, just like not null is true.
the two solutions I've listed are either or.

[dalexeev]

The error is still reproduced in 4.0 beta 1.

[dalexeev]

Related?

# 3.x
print(1 if ""  else 2) # 2
print(1 if !"" else 2) # 1

# 4.0 beta 3
print(1 if ""  else 2) # 2
print(1 if !"" else 2) # 2

[vmedea]

if [Freed Object]: should validate to false as well

I agree this is a weird situation (I came here from google, searching whether this behavior changed in 4). But also it can be useful to distingish a no-longer-existent object from a variable intentionally set (or initialized) to null. Say, we're tracking a target node, keeping this as a variable on the player. We'd want to know when it disappears. So I'm not sure it's a good idea to get rid of this distinction completely.