obcache-go

obcache.Wrap(cache, fn) returns a function of the same type. A repeat call with the same arguments returns the stored result without running fn. Concurrent callers with the same arguments, in one cache, share one call: stampede protection.

The defaults are 1000 entries, a 5 minute TTL and LRU eviction, with LFU and FIFO as options. The store is memory or Redis. Prometheus metrics sit in a separate package, so the cache alone does not link them.

A leading context.Context is not part of the key: anything that varies by user belongs in the arguments.

why it exists

Caching an expensive call by hand means a get, a set and an invalidation around every call site, usually for a query or an API request. obcache-go puts that behind the function, set up once.

what it taught

Memoizing a function is mostly deciding when two calls are the same call. The key is the wrapped function plus each argument after a leading context, encoded in full.

Wrap refuses a func or chan parameter, which has no stable encoding, until a key function is given.