Lil'Bits

Purpose

In some instances, even a simple HashMap<T> is too much for your application. The LilBitsSet is inspired by works such as smallset, sparseset and bitmap, but is incredibly simplistic with very few bells and whistles by excelling at really only one thing: HashSet<u8> semantics when your values are never > 63.

Personally, I plan to use this in my server-client library, where users can optionally choose to broadcast to a LilBitSet of clients. As no more than ~10 are expected to be online at once, a LilBitSet is perfect for reasoning over objects relating to these clients and their corresponding IDs.

Usefulness

This data structure has two severe limitations in comparison to other sets:

1. Only u8 can be stored (or any integer as u8, of course)
2. No value >= 64 can be stored. This is in constrast to smallset, where the limitation is on the number of elements, rather than the value of the elements. Chances are, if these restrictions are dealbreakers for your purpose rather use a smallset or something like it. Otherwise, LilBitSet has some excellent properties:

• Super-fast basic operations such as insert
• super fast Clone and Copy
• trivially benefits from obvious Sized,Sync, Serialize, Deserialize etc.
• set-logic leaning on super fast bitwise operations (eg union to |)

Additionally, there exists a convenience macro lilbits! for constructing a LilBitSet, as well as some potentially useful From implementations to convert back and forth to other common sets HashSet, BTreeSet.

Using It Yourself

The semantics of LilBitSet are similar to that of HashSet<u8>minus some missing functions which woudln't be useful, such as new_with_capacity.

Most noteworthy is that the thread will Panic! if there is ever an attempt to insert some u8 with a value greater than 63. If this behaviour is undesirable, just protect it with an if check. I avoided implementing it myself as it simply bloats the API.

Examples

See tests.rs for annotated examples.