smol_str

A SmolStr is a string type that has the following properties:

• size_of::<SmolStr>() == 24 (therefore == size_of::<String>() on 64 bit platforms)
• Clone is O(1) (no allocation)
• Strings are stack-allocated if they are:
  • Up to 23 bytes long
  • Longer than 23 bytes, but substrings of WS (see src/lib.rs). Such strings consist solely of consecutive newlines, followed by consecutive spaces
• If a string does not satisfy the aforementioned conditions, it is heap-allocated
• Additionally, a SmolStr can be explicitly created from a &'static str without allocation

Unlike String, however, SmolStr is immutable. The primary use case for SmolStr is a good enough default storage for tokens of typical programming languages. Strings consisting of a series of newlines, followed by a series of whitespace are a typical pattern in computer programs because of indentation. Note that a specialized interner might be a better solution for some use cases.

Benchmarks

Run criterion benches with

cargo bench --bench \* -- --quick

MSRV Policy

Minimal Supported Rust Version: latest stable.

Bumping MSRV is not considered a semver-breaking change.