import Optional from "./Optional";
export default abstract class Iterator<T> {
    done: boolean;
    constructor();
    abstract next(): Optional<T>;
    protected _done(): Optional<T>;
    _continue(obj: T): Optional<T>;
    _dirty(obj: null | undefined): Optional<T>;
    /**
     * Close iterator and free the cached resources.
     * @virtual
     */
    close(): void;
}
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