Add the ability to use custom classes in @export and Array[Type]

[hidemat]

I'm pretty sure there is a reason why this is not allowed yet, but nonetheless, just want to put it out there. This would be nice.

For example, if I make a CustomResource that extends Resource the only options that I can think of are:

1. expose it in the editor as @export var custom : Resource and then do a cast somewhere in my code custom = custom as CustomResource
2. create the CustomResource as a built-in type by making a c++ module or GDExtension. The problem with this is that not everybody is comfortable with dealing with c++ modules or GDExtensions, and it feels like overkill in terms of implementing a simple custom resource.

And it's the same situation with the Array type. If, for example, I iterate through and Array I need to cast it like so:

for element in element_array:
    element = element as CustomClass
    ...

I guess I'm ok with these workarounds, but it would be a huge plus for people that are used to static typing. It's a quality-of-life improvement. What do you guys think?

[Diddykonga]

This has been a long since discussed topic since 2019.
The PR should hopefully make it for 4.0, but if not then hopefully 4.1

Proposal: #18
PR: godotengine/godot#62411

[hidemat]

I see. Thanks for replying. I checked the proposals but not the issues.