ManagedAtomicLazyReference
がピッタリ正解なのか、これはやろうとしてることに対して過剰なのか、よくわからない/// A reference type holding a lazily initializable atomic /// strong reference, with automatic memory management. /// /// These values can be set (initialized) exactly once, but read many /// times. @_fixed_layout public class ManagedAtomicLazyReference<Instance: AnyObject> {