LeanString

Compact, clone-on-write string.

Properties

LeanString has the following properties:

• size_of::<LeanString>() == size_of::<[usize; 2]>() (2 words).
  • one usize smaller than String.
• Stores up to 16 bytes inline (on the stack).
  • 8 bytes if 32-bit architecture.
  • Strings larger than 16 bytes are stored on the heap.
• Clone-on-Write (CoW)
  • LeanString uses a reference-counted heap buffer (like Arc).
  • When a LeanString is cloned, the heap buffer is shared.
  • When a LeanString is mutated, the heap buffer is copied if it is shared.
• O(1), zero allocation construction from &'static str.
• Nich optimized for Option<LeanString>.
  • size_of::<Option<LeanString>>() == size_of::<LeanString>()
• High API compatibility for String.

TODOs

• Support 32-bit architecture.
• More API compatibility with String.
• Fuzz testing.
• Benchmarking.
• Documentation.
• etc...

Example

use lean_string::LeanString;

// This is a zero-allocation operation, stored inlined.
let small = LeanString::from("Hello");

// More than 16 bytes, stored on the heap (64-bit architecture).
let large = LeanString::from("This is a not long but can't store inlined!");

// Clone is O(1), heap buffer is shared.
let mut shared = large.clone();

// Mutating a shared string will copy the heap buffer. (CoW)
assert_eq!(shared.pop(), Some('!'));
assert_eq!(shared, "This is a not long but can't store inlined");
assert_eq!(large, shared + "!");

Which should I use?

TODO: Compare LeanString with String, EcoString, CompactString, etc...

Special Thanks

The idea and implementation of LeanString is inspired by the following projects:

• EcoString
• CompactString

I would like to thank the authors of these projects for their great work.

License

This crate is licensed under the MIT license.