import { Observable } from '../Observable';
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import { EmptyError } from '../util/EmptyError';
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import { OperatorFunction, TruthyTypesOf } from '../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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export function last<T>(predicate: BooleanConstructor): OperatorFunction<T, TruthyTypesOf<T>>;
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export function last<T, D>(predicate: BooleanConstructor, defaultValue: D): OperatorFunction<T, TruthyTypesOf<T> | D>;
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export function last<T, D = T>(predicate?: null, defaultValue?: D): 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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/**
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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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* It will throw an error if the source completes without notification or one that matches the predicate. It
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* returns the last value or if a predicate is provided last value that matches the predicate. It returns the
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* given default value if no notification is emitted or matches the predicate.
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*
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* ## Examples
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*
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* Last alphabet from the sequence
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*
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* ```ts
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* import { from, last } from 'rxjs';
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*
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* const source = from(['x', 'y', 'z']);
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* const result = source.pipe(last());
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*
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* result.subscribe(value => console.log(`Last alphabet: ${ value }`));
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*
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* // Outputs
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* // Last alphabet: z
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* ```
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*
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* Default value when the value in the predicate is not matched
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*
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* ```ts
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* import { from, last } from 'rxjs';
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*
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* const source = from(['x', 'y', 'z']);
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* const result = source.pipe(last(char => char === 'a', 'not found'));
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*
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* result.subscribe(value => console.log(`'a' is ${ value }.`));
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*
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* // Outputs
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* // 'a' is not found.
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* ```
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*
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* @see {@link skip}
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* @see {@link skipUntil}
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* @see {@link skipLast}
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* @see {@link skipWhile}
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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 A function that returns an Observable that emits only the last item
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* satisfying the given condition from the source, or a NoSuchElementException
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* 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>) =>
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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(defaultValue!) : throwIfEmpty(() => new EmptyError())
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);
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}
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