interface Array<T> {
    first: typeof first;
    findById: typeof findById;
    last: typeof last;
    exists: typeof exists;
    intersect: typeof intersect;
}
/**
 * This function returns the first element of the array, if it exists. Otherwise it returns undefined.
 * @param this The array itself
 * @returns T | undefined
 */
declare function first<T>(this: T[]): T | undefined;
/**
 * This function returns the first element of the array, if it exists. Otherwise it returns undefined.
 * @param this The array itself
 * @returns T | undefined
 */
declare function findById<T>(this: T[], id: number): T | undefined;
/**
 * This function returns the last element of the array, if it exists. Otherwise it returns undefined.
 * @param this The array itself
 * @returns T | undefined
 */
declare function last<T>(this: T[]): T | undefined;
/**
 * This function returns true, if the array exists (has more than one element).
 * @param this The array itself
 * @returns boolean
 */
declare function exists<T>(this: T[]): boolean;
/**
 * This function gets the intersects of two arrays.
 * @param this The array itself
 * @param array The relative array. The other one, that needs to check.
 * @example array.intersect(array2);
 * @returns Array<T>
 */
declare function intersect<T>(this: T[], array: T[]): T[];