@zeix/cause-effect/types/src/nodes/memo.d.ts

Cause & Effect - reactive state management primitives library for TypeScript.

import { type ComputedOptions, type MemoCallback } from '../graph';
/**
 * A derived reactive computation that caches its result.
 * Automatically tracks dependencies and recomputes when they change.
 *
 * @template T - The type of value computed by the memo
 */
type Memo<T extends {}> = {
    readonly [Symbol.toStringTag]: 'Memo';
    /**
     * Gets the current value of the memo.
     * Recomputes if dependencies have changed since last access.
     * When called inside another reactive context, creates a dependency.
     * @returns The computed value
     */
    get(): T;
};
/**
 * Creates a derived reactive computation that caches its result.
 * The computation automatically tracks dependencies and recomputes when they change.
 * Uses lazy evaluation - only computes when the value is accessed.
 *
 * @since 0.18.0
 * @template T - The type of value computed by the memo
 * @param fn - The computation function that receives the previous value
 * @param options - Optional configuration for the memo
 * @param options.value - Optional initial value for reducer patterns
 * @param options.equals - Optional equality function. Defaults to strict equality (`===`)
 * @param options.guard - Optional type guard to validate values
 * @param options.watched - Optional callback invoked when the memo is first watched by an effect.
 *   Receives an `invalidate` function to mark the memo dirty and trigger recomputation.
 *   Must return a cleanup function called when no effects are watching.
 * @returns A Memo object with a get() method
 *
 * @example
 * ```ts
 * const count = createState(0);
 * const doubled = createMemo(() => count.get() * 2);
 * console.log(doubled.get()); // 0
 * count.set(5);
 * console.log(doubled.get()); // 10
 * ```
 *
 * @example
 * ```ts
 * // Using previous value
 * const sum = createMemo((prev) => prev + count.get(), { value: 0, equals: Object.is });
 * ```
 */
declare function createMemo<T extends {}>(fn: (prev: T) => T, options: ComputedOptions<T> & {
    value: T;
}): Memo<T>;
declare function createMemo<T extends {}>(fn: MemoCallback<T>, options?: ComputedOptions<T>): Memo<T>;
/**
 * Checks if a value is a Memo signal.
 *
 * @since 0.18.0
 * @param value - The value to check
 * @returns True if the value is a Memo
 */
declare function isMemo<T extends {} = unknown & {}>(value: unknown): value is Memo<T>;
export { createMemo, isMemo, type Memo };