kstring 2.0.0

Key String: optimized for map keys


Key String: Optimized for map keys.

Crates Status



  • Large maps
  • Most keys live and drop without being used in any other way
  • Most keys are relatively small (single to double digit bytes)
  • Keys are immutable
  • Allow zero-cost abstractions between structs and maps (e.g. no allocating when dealing with struct field names)


  • Inline small strings rather than going to the heap.
  • Preserve &'static str across strings (KString), references (KStringRef), and lifetime abstractions (KStringCow) to avoid allocating for struct field names.
  • Use Box<str> rather than String to use less memory.


  • max_inline: Instead of aligning the inline-string for performance (15 bytes + length on 64-bit), use the full width (22 bytes on 64-bit)
  • arc: Instead of using Box<str>, use Arc<str>. Note: allocations are fast enough that this can actually slow things down for small enough strings.


  • smol_str
    • Size of String
    • Always uses Arc instead of Box
    • Always inlines 22 bytes
    • Whitespace-only optimizations
  • smartstring
    • Size of String
    • Allows mutability at the cost of relying on implementation details of String
    • Always inlines 23 bytes
  • compact_str
    • Size of String
    • Always uses Arc instead of Box
    • Inlines 22-23 bytes, depending on implementation


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