maplike

This crate provides traits for common operations over map-like data structures: get, insert, remove, stable remove, push.

Supported collections

Standard library

Rust's standard library collections are supported via built-in convenience implementations:

• HashMap, gated by the std feature (enabled by default);
• HashSet, gated by the std feature (enabled by default);
• BTreeMap, not feature-gated;
• BTreeSet, not feature-gated;
• Vec, not feature-gated, but does not support stable removal.

Third-party types

In addition to the standard library, maplike has built-in feature-gated convenience implementations for data structures from certain external crates:

• stable_vec::StableVec, gated by the stable-vec feature; (example usage: examples/stable_vec.rs),
• thunderdome::Arena, gated by the thunderdome feature; (example usage: examples/thunderdome.rs),
• rstar::RTree, gated by the rstar feature. (example usage: examples/rstar.rs).
• rstared::RTreed, gated by the rstared feature.

Unsupported collections

Standard library's VecDeque is unsupported.

Among stable vector data structures, Slab, SlotMap, generational-arena cannot be supported because they lack interfaces for insertion at an arbitrary key.

Technical sidenotes

Unlike maps and sets, not all stable vector data structures allow insertion and removal at arbitrary indexes regardless of whether they are vacant, occupied or out of bounds. For StableVec, we managed to implement inserting at out-of-bound indexes by changing the length before insertion using the .reserve_for() method. For thunderdome::Arena, we insert at arbitrary key directly via the .insert_at() method. Collections for which we could not achieve this are documented in the section below.

For Slab, an interface to insert at an arbitrary key is missing apparently because the freelist Slab uses to keep track of its vacant indexes is only singly-linked, not doubly-linked. Inserting an element at an arbitrary vacant index would require removing that index from the freelist. But since there is no backwards link available at a given key, doing so would require traversing the freelist from the beginning to find the position of the previous node, which would incur an overly slow O(n) time cost.