Getting 'Invalid get index' error that I can't figure out

AllTheDice

I'm using a custom, simple grid map to position actors.

In the code for the player setup, I set the position to 0, 0, then move it to the real starting spot (because at present my move_to func requires that the current cell and the new cell be different.

I get this error:

Invalid get index 'x' (on base: 'Nil')

On line 40, the first line of move_to(). This is on the setup call, made from like 16.

The weird thing is that if I hover over the variables in my code while the debugger is running, the proper values are displayed in the tooltip that pops up. It seems the problem is that it's not recognizing the Vector2 variables as Vector2, which is why I tried static typing them, but that didn't help.

I really appreciate any insight.

1  extends Sprite
2
3  var map
4
5  var map_cell: Vector2
6
7  signal player_moved
8
9  # Called when the node enters the scene tree for the first time.
10 func _ready():
11  pass
12 	
13 func setup():
14     map = get_node("../SimpleMap")
15     map_cell = Vector2(0, 0)
16     move_to(Vector2(7, 7))
17	
18 # Input event handler.
19 func _input(event):
20     var new_cell = Vector2(map_cell.x, map_cell.y)
21     if get_parent().player_turn:
22         if event is InputEventKey:
23             if event.is_action_pressed("player_left"):
24                 new_cell.x -= 1
25             elif event.is_action_pressed("player_right"):
26                 new_cell.x += 1
27             elif event.is_action_pressed("player_up"):
28                 new_cell.y -= 1
29             elif event.is_action_pressed("player_down"):
30                 new_cell.y += 1
31
32     if move_to(new_cell) > 0:
33         # If we make it here, the player has successfully moved.
34         emit_signal("player_moved")
35
36 func _process(delta):
37     pass
38	
39 func move_to(new_pos: Vector2):
40     if new_pos.x == map_cell.x and new_pos.y == map_cell.y:
41         return -1
42     # Can't move the player off the map.
43     elif new_pos.x < 0 or new_pos.x > map.size.x - 1 
44                 or new_pos.y < 0 or new_pos.y > map.size.y - 1:
44         return -2
45     # Can't move into an enemy.
46     elif map.get_cell(new_pos) != null:
47         return -3
48     else:
49         position.x = map.offset.x + map.get_cell_origin(new_pos).x
50         position.y = map.offset.y + map.get_cell_origin(new_pos).y
51         map.set_cell(map_cell, null)
52         map.set_cell(new_pos, self)
53         map_cell = new_pos
54         return 1

Megalomaniak

Your map node is likely not yet in the scene when the script first tries to run.

AllTheDice

I call setup from the parent node's _ready, which I understand only gets called after all of its children are ready. Perhaps there's a better way to do that?

Even so, apart from getting it, the codepath to my error doesn't touch the map object.

Megalomaniak

This node would be readied before it's parent though.

AllTheDice

Right, which is why I don't do the work in _ready. My work-around is to use the custom function 'setup', which only gets called once the parent (and all of its children) are ready.

TwistedTwigleg

Maybe before line 40 add something like print ("new_pos :", new_pos, " | map_cell: ", map_cell) to see which of the two variables is null? Maybe the issue is the position passed in to the function, new_pos, is null?

AllTheDice

That's good confirmation. It prints out:

new_pos: (7,7) | map_cell: (0,0)

Which matches the values reported in the debugger tool tips.

AllTheDice

Just for completeness, I changed the print line to print each coordinate individually, so the new function is:

39 func move_to(new_pos: Vector2):
40     print("new_pos: [",  new_pos.x, ", ", new_pos.y, "] | map_cell: [", map_cell.x, ", ", map_cell.y, "]")
41     if  new_pos.x == map_cell.x and new_pos.y == map_cell.y:
42         return -1
42     # Can't move the player off the map.
43     elif new_pos.x < 0 or new_pos.x > map.size.x - 1 or new_pos.y < 0 or new_pos.y > map.size.y - 1:
44         return -2
45     # Can't move into an enemy.
46     elif map.get_cell(new_pos) != null:
47         return -3
48     else:
49        position.x = map.offset.x + map.get_cell_origin(new_pos).x
50        position.y = map.offset.y + map.get_cell_origin(new_pos).y
51        map.set_cell(map_cell, null)
52        map.set_cell(new_pos, self)
53        map_cell = new_pos
54        return 1

The new line 40 works fine: the coordinates are printed in output.

But then line 41 gives me the same error. Out of curiosity, I got rid of the first if so that the map boundary checking is the first logical check. I get the same error there. For some reason, it seems like it can't get a coordinate of the Vector2 as part of a Boolean expression, which makes no sense.

I'd love to learn that I'm doing something wrong here, but I can't understand why retrieving a property works on one line and not on the next!

AllTheDice

This get weirder and weirder. I've changed the function to store the individual coordinates in local variables. Then I use the local variables to do the logical comparisons:

func move_to(new_pos: Vector2):
	print("new_pos: [",  new_pos.x, ", ", new_pos.y, "] | map_cell: [", map_cell.x, ", ", map_cell.y, "]")
	
	var old_x = map_cell.x
	var old_y = map_cell.y
	var new_x = new_pos.x
	var new_y = new_pos.y
	
	print("[", old_x, ", ", old_y, "], [", new_x, ", ", new_y, "]")
	
	if new_x == old_x and new_y == old_y:
		return -1
	# Can't move the player off the map.
	elif new_pos.x < 0 or new_pos.x > map.size.x - 1 or new_pos.y < 0 or new_pos.y > map.size.y - 1:
		return -2
	# Can't move into an enemy.
	elif map.get_cell(new_pos) != null:
		return -3
	else:
		position.x = map.offset.x + map.get_cell_origin(new_pos).x
		position.y = map.offset.y + map.get_cell_origin(new_pos).y
		map.set_cell(map_cell, null)
		map.set_cell(new_pos, self)
		map_cell = new_pos
		return 1

Everything prints out exactly as I expect it to--all the values are as they should be. But when it gets to the logical test (line 11), I get the same error! And now there's nothing on that line trying to access index 'x' of anything. So confused...

TwistedTwigleg

Maybe the issue is not with one of the elif statements instead, but since the if statement is the beginning of the set of conditions, the debugger is flagging the if rather than the elif causing the issue? If that is the case, then the only thing I can think of is that map.size is null, since the error says the issue is accessing the x variable.

AllTheDice

You seem to be right. Even though the little green arrow that indicates the position in the code is pointing to the if, it's bombing on map.size.x.

Now to trace that down. Thanks!