An SKAction that writes a value to a specified object.

SKAction+Keypath.swift

extension SKAction {
    static func write<Root: AnyObject, Value>(
        value: Value,
        to keyPath: ReferenceWritableKeyPath<Root, Value>,
        on object: Root
    ) -> SKAction {
        SKAction.customAction(withDuration: 0) { [weak object] _, _ in
            object?[keyPath: keyPath] = value
        }
    }
}