Crate string_cache

source ·
Expand description

A library for interning things that are AsRef<str>.

Some strings may be interned at compile time using the string-cache-codegen crate, or the EmptyStaticAtomSet may be used that has no compile-time interned strings. An Atom is an interned string for a given set (either EmptyStaticAtomSet or a generated StaticAtomSet).

Generated Atoms will have assocated macros to intern static strings at compile-time.


Here are two examples, one with compile-time Atoms, and one without.

§With compile-time atoms

In Cargo.toml:

string_cache = "0.8"

string_cache_codegen = "0.5"


extern crate string_cache_codegen;

use std::env;
use std::path::Path;

fn main() {
    string_cache_codegen::AtomType::new("foo::FooAtom", "foo_atom!")
        .atoms(&["foo", "bar"])


extern crate string_cache;

mod foo {
    include!(concat!(env!("OUT_DIR"), "/"));

fn use_the_atom(t: &str) {
    match *t {
        foo_atom!("foo") => println!("Found foo!"),
        foo_atom!("bar") => println!("Found bar!"),
        // foo_atom!("baz") => println!("Found baz!"), - would be a compile time error
        _ => {
            println!("String not interned");
            // We can intern strings at runtime as well

§No compile-time atoms

use string_cache::DefaultAtom;

let mut interned_stuff = Vec::new();
let text = "here is a sentence of text that will be tokenised and
            interned and some repeated tokens is of text and";
for word in text.split_whitespace() {
    let seen_before = interned_stuff.iter()
        // We can use impl PartialEq<T> where T is anything string-like
        // to compare to interned strings to either other interned strings,
        // or actual strings  Comparing two interned strings is very fast
        // (normally a single cpu operation).
        .filter(|interned_word| interned_word == &word)
    if seen_before > 0 {
        println!(r#"Seen the word "{}" {} times"#, word, seen_before);
    } else {
        println!(r#"Not seen the word "{}" before"#, word);
    // We use the impl From<(Cow<'a, str>, or &'a str, or String)> for
    // Atom<Static> to intern a new string.




Type Aliases§

  • Use this if you don’t care about static atoms.