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patch

@rotorsoft/act-root

@rotorsoft/act-root / act-patch/src / patch

Function: patch()

patch<S>(original, patches): Readonly<S>

Defined in: libs/act-patch/src/patch.ts:25

Immutably deep-merges patches into original.

This is a pure function — it never mutates its arguments and always returns a deterministic result for the same inputs.

Merging rules:

  • Plain objects: Deep merge recursively
  • Arrays, Dates, RegExp, Maps, Sets, TypedArrays: Replace entirely
  • undefined or null values: Delete the property
  • Primitives: Replace with patch value

Structural sharing: Unpatched subtrees are reused by reference, not deep-copied. This is safe because Act state is always Readonly<S> and events are immutable — state is only ever updated through new patches. This is the same approach used by Immer, Redux Toolkit, and other immutable state libraries.

Type Parameters​

S​

S extends Schema

Parameters​

original​

Readonly<S>

The original state object to patch (not mutated)

patches​

Readonly<Patch<S>> | null | undefined

The patches to apply (recursive partial of the state shape)

Returns​

Readonly<S>

A new state object with patches applied, sharing unpatched subtree references