import Sequence from "./Sequence";
export declare class First {
    /**
     * Returns the first element of the sequence or the first element matching `predicate` if present, otherwise throws
     * an error.
     *
     * @param {(T) => boolean} predicate
     * @returns {T}
     */
    first<T>(this: Sequence<T>, predicate?: (item: T) => boolean): T;
}