forExpires

forExpires is a term used in software design to describe a contract that attaches an expiration policy to a resource, such as a cache entry, a session token, or temporary data. The concept separates the content from its lifetime, enabling predictable invalidation and resource reclamation.

Core components typically include:

- expiryTime: a timestamp after which the resource is considered expired.

- ttl (time-to-live): a duration used to compute expiryTime from an origin time.

- policy: determines how expiry behaves, commonly absolute (fixed expiry) or sliding (extends on access).

- lastAccess or lastRenewal: records the most recent access or renewal event.

- renewal hook: an optional function to refresh or revalidate the resource before expiration.

Behavior: isExpired(now) returns true if now is at or past expiryTime. On access, a sliding policy may call renew(...) to push expiryTime forward. On expiration, a cleanup action or resource invalidation may be triggered.

Applications: forExpires is used in caching layers, session management, and temporary tokens, where predictable lifetimes help coordinate eviction and renewal.

Implementation notes: use a consistent time source, handle clock skew, store expiry state with the resource, and ensure thread-safety in concurrent environments. Consider serialization formats for persistence and the interaction with distributed systems.

Variants and related terms: absolute vs sliding expiration; TTL; renewal strategies; refresh tokens.

See also: caching, token expiration, expiration policies, TTL.