Crate compact_str

compact_str

A memory efficient string type that can store up to 24* bytes on the stack.

_{* 12 bytes for 32-bit architectures}

About

A CompactString is a more memory efficient string type, that can store smaller strings on the stack, and transparently stores longer strings on the heap (aka a small string optimization). It can mostly be used as a drop in replacement for String and are particularly useful in parsing, deserializing, or any other application where you may have smaller strings.

Properties

A CompactString specifically has the following properties:

• size_of::<CompactString>() == size_of::<String>()
• Stores up to 24 bytes on the stack
  • 12 bytes if running on a 32 bit architecture
• Strings longer than 24 bytes are stored on the heap
• Clone is O(n)
• From<String> or From<Box<str>> re-uses underlying buffer
  • Eagerly inlines small strings
• O(1) creation from &'static str with CompactString::const_new
• Heap based string grows at a rate of 1.5x
  • The std library String grows at a rate of 2x
• Space optimized for Option<_>
  • size_of::<CompactString>() == size_of::<Option<CompactString>>()
• Uses branchless instructions for string accesses
• Supports no_std environments

Traits

This crate exposes two traits, ToCompactString and CompactStringExt.

ToCompactString

Provides the to_compact_string(&self) method for converting types into a CompactString. This trait is automatically implemented for all types that are std::fmt::Display, with specialized higher performance impls for:

• u8, u16, u32, u64, usize, u128
• i8, i16, i32, i64