export declare namespace ArrayUtils {
    interface Head<T> extends Array<T> {
        head(): T;
    }
    interface Tail<T> extends Array<T> {
        tail(): T;
    }
    interface Children<T> extends Array<T> {
        children(): Tail<T>;
    }
    const TailImpl: {
        tail<T>(this: Array<T>): T;
    };
    const HeadAndChildrenImpl: {
        head<T>(this: Array<T>): T;
        children<T_1>(this: T_1[]): Tail<T_1>;
    };
    interface HeadAndTail<T> extends Head<T>, Tail<T>, Children<T> {
    }
    function asTail<T>(array: Array<T>): Tail<T>;
    function asHeadAndTail<T>(array: Array<T>): HeadAndTail<T>;
    enum Sort {
        LeftBeforeRight = -1,
        RightBeforeLeft = 1,
        Equal = 0
    }
    /**
     * Performs a binary search algorithm over a sorted collection. Useful for cases
     * when we need to perform a binary search over something that isn't actually an
     * array, and converting data to an array would defeat the use of binary search
     * in the first place.
     *
     * @param length The collection length.
     * @param compareToKey A function that takes an index of an element in the
     *   collection and returns zero if the value at this index is equal to the
     *   search key, a negative number if the value precedes the search key in the
     *   sorting order, or a positive number if the search key precedes the value.
     * @return A non-negative index of an element, if found. If not found, the
     *   result is -(n+1) (or ~n, using bitwise notation), where n is the index
     *   where the key should be inserted to maintain the sorting order.
     */
    function binarySearch2(length: number, compareToKey: (index: number) => number): number;
    function partition<T>(array: T[], filter: (e: T, idx: number, arr: T[]) => boolean | undefined): [T[], T[]];
    /**
     * @returns New array with all falsy values removed. The original array IS NOT modified.
     */
    function coalesce<T>(array: ReadonlyArray<T | undefined | null>): T[];
    /**
     * groups array elements through a comparator function
     * @param data array of elements to group
     * @param compare comparator function: return of 0 means should group, anything above means not group
     * @returns array of arrays with grouped elements
     */
    function groupBy<T>(data: ReadonlyArray<T>, compare: (a: T, b: T) => number): T[][];
}
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