flagsChanged

flagsChanged is a term used in software engineering to denote an event, notification, or callback that occurs when a set of bitwise flags changes. A flags variable is typically a bitmask in which each bit represents a discrete option or feature. When the value of the bitmask changes, an implementation may raise a flagsChanged signal to inform interested components about the update.

Change detection can be implemented in various ways: a property setter, an atomic update, or a dedicated change-detection function. Observers commonly receive the old and new values, or a mask detailing which bits changed. In many designs the event is emitted only if the new value differs from the old value; some implementations may also provide a changedBits mask to indicate exactly which flags were altered.

Observers subscribe to flagsChanged to react to enable/disable of features, UI state updates, or configuration reconfiguration. It is used in feature flag systems, hardware interface layers, and protocol handling where a set of boolean options is tracked in a single integer or similar structure.

Practical considerations include thread-safety, avoiding re-entrancy problems, and ensuring a consistent change order when multiple code paths update the flags concurrently. Clear documentation of what constitutes a change and what data is delivered (old/new values, changedBits) helps reduce confusion and improve reliability.

See also: bitmask, feature flags, property change notification, observer pattern, signals and slots, KVO, event-driven design.