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.)
Fortunately, we can do better than these things in Rust. Our type system is quite equal to easy, robust expression of such problems.
The AnyMap type is a friendly wrapper around a HashMap<TypeId, Box<Any>>, exposing a nice, easy typed interface, perfectly safe and absolutely robust.
What this means is that in an AnyMap you may store zero or one values for every type.
Cargo all the way: it is anymap on crates.io.
There is an optional clone feature on the anymap crate; if enabled, your AnyMap will require contained types to implement Clone and will itself satisfy Clone.
For users of the nightly instead of the beta of rustc there are a couple of things behind the nightly feature like a drain method on the RawAnyMap and a more efficient hashing technique which makes lookup in the map a tad faster.
Chris Morgan (chris-morgan) is the primary author and maintainer of AnyMap.
This library is distributed under similar terms to Rust: dual licensed under the MIT license and the Apache license (version 2.0).
See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.