Only "String" or "StringName" can be used as index for type "JSON", but received "int"

[tibaverus]

Godot Version

v4.4.1.stable.official [49a5bc7b6]

Question

I’m a little confused about this error message that I received. I’ve only ever used C# before so if this is somehow expected behaviour in GDScript then I’d love to know why.

The following code, according to Godot, is incorrect:

var json: JSON = response.body_as_json()
var monster: Monster = JsonToMonster(json[0])

However, this code, is apparently perfectly fine:

var json: JSON = response.body_as_json()
for jsonEntry in json:
	var monster: Monster = JsonToMonster(jsonEntry)

My function called JsonToMonster’s signature looks like this:

func JsonToMonster(json: JSON) -> Monster:

Why is the second option “correct” but the first one isn’t? And how can I make the first one work, because I need to pick a specific element in some cases.
I understand the error message itself, it’s expecting a string to identify part of the Json, but why can’t it accept an int?

[Windows98]

My guess is that because of how Json sort of work like dictionaries where they store data with keys (in the form of strings) referring to them.

Like:

{
    "key1" : {
        "item1",
        "item2"
    }
}

I’m not sure how it works in GdScript but in c# when using dictionary you’d have to do something like “dictionary[“key1”]” as opposed to “dictionary[0]”.

Might be why you can’t use indexes in this context. Tho I could be wrong since I do not use GDScript and I am not particularly familiar with it.

[tibaverus]

Not always, the example you showed me can happen, but in my case, the json file looks like this:

[
  {
    "id": 1,
    "monsterName": "RedactedCuzNDA",
    "otherStuffEtc...": 100,
   },
   {
      "id": 2,
      "monsterName": "RedactedCuzNDA",
      "otherStuffEtc...": 200,
   },
]

[Windows98]

Then you might have to convert it to an array of Json objects? Then maybe you could use indexers.

[Windows98]

If i remember correctly, converting this Json object to a Variant in Godot would result in an Array of Dictionaries which you could then use indexers and instantiate your monsters from said Dictionaries.

There might be a better way to do it, like I said, not the most knowledgeable when it comes to GDScript.

[tibaverus]

@Windows98

If i remember correctly, converting this Json object to a Variant in Godot would result in an Array of Dictionaries

Turns out this is correct. It seems I can get back a simple Array, so doing this more or less achieves what I originally wanted:

var json: Array = response.body_as_json()
var monster: Monster = JsonToMonster(json[0])

Although it’s really odd that this is no longer considered a JSON object, for example, in this case, json[0] is now a Dictionary, not JSON.

So the function name body_as_json doesn’t exactly do what one would expect from the name.

But also, interestingly enough, if I do what I did originally:

var json: JSON = response.body_as_json()
for jsonEntry in json:
	var monster: Monster = JsonToMonster(jsonEntry)

This is still a json, and the object I get in my JsonToMonster function is, indeed, a JSON object. So I’m not sure what’s going on here?

[Windows98]

I assume this is because Godot has implicit casting for Json to Arrays.

Sort of like how you can do:

var test: StringName = "string_name"
var test2: string = test

Or:

var num: int = 1
var num2: float = num

The above example works totally even tho the values assigned does have the same types, the engine just knows how to cast one to another.

[tibaverus]

Ahh yes, I’m starting to remember why I dropped JS as well and went with C# for almost everything in my life hah.

But anyway, I more or less get why it happens, even if I don’t really agree with it, thank you for the help!

[mrcdk]

A JSON object can be a collection of key/value pairs or a list of values. From JSON

JSON is built on two structures:

• A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
• An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.

Because of this, in Godot, a JSON object can be represented by Dictionary or an Array then, because it can be both, the different ways to parse a JSON string returns a Variant

You can know at runtime if its a Dictionary or an Array with @GlobalScope.typeof() or by using the is keyword like:

if value is Dictionary:
    pass
elif value is Array:
    pass