import { JSONPrimitive } from '../types';
/**
 * @private
 */
export type JSONValuePlusUndefined = JSONPrimitive | undefined | JSONValuePlusUndefined[] | JSONObjectWithUndefined;
/**
 * @private
 */
export type JSONObjectWithUndefined = {
    [K: string]: JSONValuePlusUndefined;
};
/**
 * @private
 */
export type NestedObject<Leaf> = {
    [K: string]: MaybeNestedObject<Leaf>;
};
/**
 * @private
 */
export type MaybeNestedObject<Leaf> = Leaf | NestedObject<Leaf>;
/**
 * Deep merge source into target, returning shallow copies to keep unchanged identities
 * stable.
 *
 * @private
 */
export declare function merge<Leaf extends JSONValuePlusUndefined, RLeaf = Leaf>(target: NestedObject<Leaf>, source: NestedObject<Leaf | undefined>): NestedObject<RLeaf>;