Sure!
I'm working on a cross platform Swift Package that makes using gravity a 1 liner for Swift projects, here.

TLDR Question:
How do I add instance variables to a gravity_class_t using the C API?

Long Question:
I'm trying to allow Swift to describe a Gravity Class.
The documentation shows how to add a function and that's easy enough and I was able to do that no problem.

To add an instance variable, I currently have this from browsing the Gravity source:

let index = gravity_class_add_ivar(gravityClass, name)
let function = gravity_function_new_special(nil, nil, UInt16(index), nil, nil)
let closure = gravity_closure_new(gravity.vm, function)
gravity_class_bind(gravityClass, name, gravity_value_from_object(closure))

However when attempting to retrieve the value from an instance, here, the closure.f is no longer referencing the function.
_{This value retrieval works fine for instances that Gravity creates from a script.}

I wrote a test with a full example of the failure and how I'm using it.

func testHostCreateClientClass() throws {        
    let theThingClass = gravity.createClass(named: "TheThing")
    theThingClass.addInstanceVariable(named: "myVar")
        
    try gravity.compile("extern class TheThing; var theThing = TheThing(); func main() {}")
    try gravity.runMain()
        
    let instance = try gravity.getInstance("theThing")
    
    let gValue = gravity.createValue(randomValue)
    instance.setValue(gValue, named: "myVar")
    
    let result = instance.getValue("myVar")
        
    XCTAssertEqual(result.getInt(), randomValue)
}

@marcobambini
Fixed.
I thought I was missing a step here, but my issue was from the use of gravity_closure_free in an unrelated location earlier on.