Crate fastcache

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fastcache Documentation License Build Status

A performant but not-so-accurate time and capacity based cache for Rust.

This crate provides an implementation of a time-to-live (TTL) and capacity based cache. It stores key-value pairs and automatically evicts expired entries based on their TTL.

The design trades off exact TTL-based expiration for better performance, which means that expired items may not be removed immediately upon expiration, and an item may be removed before its expiration time.

It’s also by design that get may return expired items, which means that the caller should check the expiration status of the returned value by calling value.is_expired() before using it. It’s up to the user if to use the expired value or not.

This design can be useful in some cases, for example, when the caller wants to use the expired value as a fallback or to do rpc in background to update the value and return the expired value immediately to reduce latency.


use fastcache::Cache;
use std::time::Duration;

let cache = Cache::new(3, Duration::from_secs(3600)); // Capacity: 3, TTL: 1 hour
cache.insert("key1", "value1");
cache.insert("key2", "value2");

if let Some(value) = cache.get("key1") {
    println!("Value: {}", value.get());
} else {
    println!("Value not found");


fastcache is dual-licensed under the MIT license and the Apache License (Version 2.0).


Any kinds of contributions are welcomed. Feel free to open pull requests or issues.


  • A not so accurate but performant time and capacity based cache.
  • A capacity based fifo cache.
  • Represents an entry in the cache.