import { Observable } from '../Observable';
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import { Operator } from '../Operator';
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import { Subscriber } from '../Subscriber';
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import { EmptyError } from '../util/EmptyError';
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import { OperatorFunction } from '../../internal/types';
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import { filter } from './filter';
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import { takeLast } from './takeLast';
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import { throwIfEmpty } from './throwIfEmpty';
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import { defaultIfEmpty } from './defaultIfEmpty';
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import { identity } from '../util/identity';
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/* tslint:disable:max-line-length */
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export function last<T, D = T>(
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predicate?: null,
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defaultValue?: D
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): OperatorFunction<T, T | D>;
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export function last<T, S extends T>(
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predicate: (value: T, index: number, source: Observable<T>) => value is S,
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defaultValue?: S
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): OperatorFunction<T, S>;
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export function last<T, D = T>(
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predicate: (value: T, index: number, source: Observable<T>) => boolean,
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defaultValue?: D
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): OperatorFunction<T, T | D>;
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/* tslint:enable:max-line-length */
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/**
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* Returns an Observable that emits only the last item emitted by the source Observable.
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* It optionally takes a predicate function as a parameter, in which case, rather than emitting
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* the last item from the source Observable, the resulting Observable will emit the last item
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* from the source Observable that satisfies the predicate.
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*
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* 
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*
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* @throws {EmptyError} Delivers an EmptyError to the Observer's `error`
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* callback if the Observable completes before any `next` notification was sent.
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* @param {function} [predicate] - The condition any source emitted item has to satisfy.
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* @param {any} [defaultValue] - An optional default value to provide if last
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* predicate isn't met or no values were emitted.
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* @return {Observable} An Observable that emits only the last item satisfying the given condition
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* from the source, or an NoSuchElementException if no such items are emitted.
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* @throws - Throws if no items that match the predicate are emitted by the source Observable.
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*/
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export function last<T, D>(
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predicate?: ((value: T, index: number, source: Observable<T>) => boolean) | null,
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defaultValue?: D
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): OperatorFunction<T, T | D> {
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const hasDefaultValue = arguments.length >= 2;
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return (source: Observable<T>) => source.pipe(
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predicate ? filter((v, i) => predicate(v, i, source)) : identity,
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takeLast(1),
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hasDefaultValue ? defaultIfEmpty<T | D>(defaultValue) : throwIfEmpty(() => new EmptyError()),
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);
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}
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