Cache

A coroutine-based in-memory cache with composable behaviours. Thread-safe, multiplatform, and designed for hot paths.

Why a custom cache?

Most JVM caches (Caffeine, Guava) are excellent but JVM-only. When you need the same caching API in commonMain for code shared between JVM and JS, your options narrow quickly. Cache fills that gap with a clean builder DSL and composable behaviours that work on all Kotlin platforms.

The core idea: composable behaviours, async eviction

Instead of one cache with many configuration flags, Cache uses composable behaviours. Stack them to get exactly the policy you need. Eviction runs asynchronously in a coroutine background loop — reading and writing the cache is fast because the calling thread never pays for eviction work.

val cache = fastCache<String, UserProfile> {
    expireAfterWrite(10.minutes)         // evict 10 min after last write
    maxEntries(1000)                      // LRU after 1000 entries
    onEviction { key, _ ->                // react to evictions
        logger.debug("evicted $key")
    }
}

cache.put("user:42", fetchUser("42"))

val user = cache.getOrPut("user:99") {
    fetchUser("99")  // only called on miss
}

Behaviour matrix

Seven behaviours, four eviction strategies, two observers, one async refresh:

What you get