If you’re familiar with Go and Go web frameworks, you may have come across the common “environment” pattern for storing data related to the request. It’s typically something like ``map[string]interface{}`` and is accessed with arbitrary strings which may clash and type assertions which are a little unwieldy and must be used very carefully. (Personally I would consider that it is just *asking* for things to blow up in your face.) In a language like Go, lacking in generics, this is the best that can be done; such a thing cannot possibly be made safe without generics.
As another example of such an interface, JavaScript objects are exactly the same—a mapping of string keys to arbitrary values. (There it is actually *more* dangerous, because methods and fields/attributes/properties are on the same plane.)
The ``AnyMap`` type is a friendly wrapper around a ``HashMap<TypeId,Box<Any>>``, exposing a nice, easy typed interface, perfectly safe and absolutely robust.
For users of the nightly instead of the beta of rustc there are a couple of things behind the `unstable` feature like a `drain` method on the `RawAnyMap` and a more efficient hashing technique which makes lookup in the map a tad faster.
