watcheddepends

Watcheddepends is a pattern in software engineering describing a mechanism for tracking dependencies and triggering recomputation when inputs change. It is designed to support incremental computation by focusing work only on components affected by a change.

Implementation typically involves a dependency graph where nodes represent data or computations and edges denote dependency relationships. The system maintains a set of watched dependencies by subscribing to change events from underlying resources such as files, databases, or configuration sources. When a dependency changes, the framework marks affected nodes as dirty and reevaluates them in a safe order, reusing cached results where possible to avoid full rebuilds. This often requires careful handling of cycles, nondeterministic inputs, and partial updates to ensure correctness.

Applications span build systems, live documentation generation, data pipelines, and configuration management. Benefits include faster feedback cycles, lower resource usage, and improved reproducibility. Challenges include keeping the watch set accurate as the environment evolves and ensuring determinism when dependencies may change asynchronously.

Watcheddepends is related to traditional dependency tracking, incremental build tools, and reactive programming patterns. It shares goals with file watchers and content-addressable caching, but emphasizes the end-to-end propagation of changes through a dependency graph.

See also incremental computation, dependency graph, file system event notification.