Atomic(T)

A value that may be updated atomically.

• If T is a reference type, or a union type containing only reference types or Nil, then only #compare_and_set, #swap, #set, #lazy_set, #get, and #lazy_get are available.
• If T is a pointer type, then the above methods plus #max and #min are available.
• If T is a non-union primitive integer type or enum type, then all operations are supported.