deltatype

Delta-type, or deltatype, is a conceptual data construct used in software engineering to represent the changes needed to transform one state into another. It is a parametric data type, Delta<T>, that encodes operations or patches to apply to a base value of type T to reach a target value. It is used for incremental edits, synchronization, versioning, and event sourcing.

A deltatype consists of change operations such as add, remove, replace, or domain-specific actions, and may include metadata like base version or patch id. Core functions include apply(base) -> target, compose(delta1, delta2) -> delta12, and invert(delta) -> delta^-1, enabling reversible and composable changes.

Common examples include text diffs, which describe inserted or deleted characters, and JSON patches that specify adds, removes, or replaces fields. In distributed systems deltatype supports delta-based synchronization and underlies concepts such as delta-CRDTs and event-sourced histories.

Advantages include reduced bandwidth and incremental saves; limitations include the need for a consistent base state and the complexity of patch generation and application. Delta types relate to diffs, patches, version histories, and change logs, and are implemented with standard or custom patch formats.