import { DropKeyMatcher } from './drop-keys.function.js';
import { MergeTuple } from './tuple.type.js';
export interface DeepMergeOptions {
    /**
     * When set to true, if any of the sources set something to undefined
     * @default false
     */
    preferUndefined?: boolean;
    /**
     * Wether or not to drop undefineds from the resulting merge before return
     * When set to true it will drop keys that are set to undefined.
     * When set to a matcher function it will drop only those keys.
     *
     * To use this functionally elsewhere see the
     * [`dropKeys`](./drop-keys.function.ts) function.
     *
     * This will happen at the last step
     *
     * @default false
     */
    dropKeys?: boolean | DropKeyMatcher;
}
/**
 * Merges multiple objects in order into a copy of the first one.
 * Arrays are merged naively using === equality.
 *
 * A key that a later source sets to `undefined` is `undefined` in the result,
 * unless the `dropKeys` option drops it.
 */
export declare const deepMerge: <T extends unknown[]>(sources: [...T], options?: DeepMergeOptions) => MergeTuple<T>;
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