@langchain/langgraph/dist/state/values/delta.js

LangGraph

//#region src/state/values/delta.ts
/**
* Symbol for runtime identification of DeltaValue instances.
*/
const DELTA_VALUE_SYMBOL = Symbol.for("langgraph.state.delta_value");
/**
* Represents a state field backed by a {@link DeltaChannel}.
*
* Unlike {@link ReducedValue} (which stores the full accumulated value in every
* checkpoint blob via `BinaryOperatorAggregate`), a `DeltaValue` field persists
* only per-step deltas (plus periodic snapshots) and reconstructs its state on
* read by replaying ancestor writes through a batch reducer. This avoids
* re-serializing large accumulators (e.g. long message histories) at every step.
*
* @remarks Beta. The on-disk representation backing `DeltaChannel` may change in
* future releases.
*
* @template Value - The type of the value stored in state and produced by reduction.
* @template Input - The type of updates accepted by the reducer.
*
* @example
* ```ts
* import { z } from "zod";
* import { StateSchema, DeltaValue } from "@langchain/langgraph";
*
* const State = new StateSchema({
*   history: new DeltaValue(z.array(z.string()).default(() => []), {
*     inputSchema: z.string(),
*     reducer: (current, writes) => [...current, ...writes],
*   }),
* });
* ```
*/
var DeltaValue = class {
	/**
	* Instance marker for runtime identification.
	* @internal
	*/
	[DELTA_VALUE_SYMBOL] = true;
	/**
	* The schema that describes the type of value stored in state (after
	* reduction). Its default (if any) seeds the channel's initial value.
	*/
	valueSchema;
	/**
	* The schema used to validate reducer inputs. Defaults to `valueSchema` when
	* not specified explicitly.
	*/
	inputSchema;
	/**
	* The batch reducer that folds a list of incoming writes into the current
	* accumulated value.
	*/
	reducer;
	/**
	* Snapshot cadence forwarded to the underlying {@link DeltaChannel}.
	*/
	snapshotFrequency;
	/**
	* Optional extra fields to merge into the generated JSON Schema.
	*/
	jsonSchemaExtra;
	constructor(valueSchema, init) {
		this.reducer = init.reducer;
		this.valueSchema = valueSchema;
		this.inputSchema = "inputSchema" in init ? init.inputSchema : valueSchema;
		this.snapshotFrequency = init.snapshotFrequency;
		this.jsonSchemaExtra = init.jsonSchemaExtra;
	}
	static isInstance(value) {
		return typeof value === "object" && value !== null && DELTA_VALUE_SYMBOL in value && value[DELTA_VALUE_SYMBOL] === true;
	}
};
//#endregion
export { DeltaValue };

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