| NULL | = | Object.new | Various classes within allows for nil values to be stored, so a special NULL token is required to indicate the "nil-ness". | |
| Array | = | ::Array | Because MRI never runs code in parallel, the existing non-thread-safe structures should usually work fine. | |
| Hash | = | ::Hash | ||
| ConcurrentCacheBackend | = | if defined?(RUBY_ENGINE) | ||
| VERSION | = | "0.3.6" |