import type { Callback } from '../../types/Callback.js';
import type { Comparer } from '../../types/Comparer.js';
import type { Group } from '../../types/Group.js';
declare global {
    interface ReadonlyArray<T> {
        /**
         * Calls a defined callback function on each element of an array, and
         * returns a new array of groups keyed by the return value of the callback
         * function, associated with an array of elements that have the same key.
         *
         * @param keyExtractFn - A function that accepts up to three arguments. The
         *  groupBy method calls the keyFn function one time for each
         *  element in the array.
         * @param keyComparerFn - An optional function that accepts two arguments.
         *  The groupBy method calls the keyComparerFn function to determine the
         *  equality of keys. Triple equal `===` comparison is used by default.
         *
         * @returns An array of group elements, each with an array of elements
         *  matching each key.
         */
        groupBy<K>(keyExtractFn: Callback<T, K>, keyComparerFn?: Comparer<K>): Array<Group<K, T>>;
    }
    interface Array<T> {
        /**
         * Calls a defined callback function on each element of an array, and
         * returns a new array of groups keyed by the return value of the callback
         * function, associated with an array of elements that have the same key.
         *
         * @param keyExtractFn - A function that accepts up to three arguments. The
         *  groupBy method calls the keyFn function one time for each
         *  element in the array.
         * @param keyComparerFn - An optional function that accepts two arguments.
         *  The groupBy method calls the keyComparerFn function to determine the
         *  equality of keys. Triple equal `===` comparison is used by default.
         *
         * @returns An array of group elements, each with an array of elements
         *  matching each key.
         */
        groupBy<K>(keyExtractFn: Callback<T, K>, keyComparerFn?: Comparer<K>): Array<Group<K, T>>;
    }
}