Important note: this article is outdated! Go to http://zsiciarz.github.io/24daysofrust/ for a recent version of all of 24 days of Rust articles. The blogpost here is kept as it is for historical reasons.

In this article we will focus on the anymap crate by Chris Morgan of rust-http and teepee fame. This crate provides the AnyMap type - a slightly peculiar, interesting container.

The AnyMap type is different from a regular map. For example, a HashMap in Rust is a generic type parametrized by K - the type of keys and V - the type of values stored in map. (There's also a hasher parameter, but it's not relevant here.) Meanwhile, AnyMap itself is not a generic type. It uses a HashMap internally but we don't need to know that; conceptually, AnyMap maps from types to values. This means that for each and every type there can be at most one value contained in the mapping.