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#291 in Data structures

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Used in 16 crates (via tinystr-macros)


145 lines

tinystr crates.io Build Status Coverage Status

tinystr is a small ASCII-only bounded length string representation.


use tinystr::{TinyStr4, TinyStr8, TinyStr16, TinyStrAuto};

fn main() {
    let s1: TinyStr4 = "tEsT".parse()
        .expect("Failed to parse.");

    assert_eq!(s1, "tEsT");
    assert_eq!(s1.to_ascii_uppercase(), "TEST");
    assert_eq!(s1.to_ascii_lowercase(), "test");
    assert_eq!(s1.to_ascii_titlecase(), "Test");
    assert_eq!(s1.is_ascii_alphanumeric(), true);

    let s2: TinyStr8 = "New York".parse()
        .expect("Failed to parse.");

    assert_eq!(s2, "New York");
    assert_eq!(s2.to_ascii_uppercase(), "NEW YORK");
    assert_eq!(s2.to_ascii_lowercase(), "new york");
    assert_eq!(s2.to_ascii_titlecase(), "New york");
    assert_eq!(s2.is_ascii_alphanumeric(), false);

    let s3: TinyStr16 = "metaMoRphosis123".parse()
        .expect("Failed to parse.");

    assert_eq!(s3, "metaMoRphosis123");
    assert_eq!(s3.to_ascii_uppercase(), "METAMORPHOSIS123");
    assert_eq!(s3.to_ascii_lowercase(), "metamorphosis123");
    assert_eq!(s3.to_ascii_titlecase(), "Metamorphosis123");
    assert_eq!(s3.is_ascii_alphanumeric(), true);

    let s4: TinyStrAuto = "shortNoAlloc".parse().unwrap();
    assert!(matches!(s4, TinyStrAuto::Tiny { .. }));
    assert_eq!(s4, "shortNoAlloc");

    let s5: TinyStrAuto = "longFallbackToHeap".parse().unwrap();
    assert!(matches!(s4, TinyStrAuto::Heap { .. }));
    assert_eq!(s4, "shortNoAlloc");


The crate provides three structs and an enum:

  • TinyStr4 an ASCII-only string limited to 4 characters.
  • TinyStr8 an ASCII-only string limited to 8 characters.
  • TinyStr16 an ASCII-only string limited to 16 characters.
  • TinyStrAuto (enum):
    • Tiny when the string is 16 characters or less.
    • Heap when the string is 17 or more characters.

The structs stores the characters as u32/u64/u128 and uses bitmasking to provide basic string manipulation operations:

  • is_ascii_numeric
  • is_ascii_alphabetic
  • is_ascii_alphanumeric
  • to_ascii_lowercase
  • to_ascii_uppercase
  • to_ascii_titlecase
  • PartialEq

TinyStrAuto stores the string as a TinyStr16 when it is short enough, or else falls back to a standard String. You should use TinyStrAuto when you expect most strings to be 16 characters or smaller, but occasionally you receive one that exceeds that length. Unlike the structs, TinyStrAuto does not implement Copy.

This set is sufficient for certain classes of uses such as unic-langid libraries.


Disable the std feature of this crate to make it #[no_std]. Doing so disables TinyStrAuto. You can re-enable TinyStrAuto in #[no_std] mode by enabling the alloc feature.


For those uses, TinyStr provides performance characteristics much better than the regular String.


The crate is fully functional and ready to be used in production. The capabilities can be extended.


Licensed under either of Apache License, Version 2.0 or MIT license at your option.

No runtime deps


  • std