import { Operator } from '../Operator';
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import { Subscriber } from '../Subscriber';
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import { Observable } from '../Observable';
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import { OperatorFunction } from '../types';
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/**
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* Emits the given constant value on the output Observable every time the source
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* Observable emits a value.
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*
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* <span class="informal">Like {@link map}, but it maps every source value to
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* the same output value every time.</span>
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*
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* 
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*
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* Takes a constant `value` as argument, and emits that whenever the source
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* Observable emits a value. In other words, ignores the actual source value,
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* and simply uses the emission moment to know when to emit the given `value`.
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*
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* ## Example
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* Map every click to the string 'Hi'
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* ```ts
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* import { fromEvent } from 'rxjs';
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* import { mapTo } from 'rxjs/operators';
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*
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* const clicks = fromEvent(document, 'click');
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* const greetings = clicks.pipe(mapTo('Hi'));
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* greetings.subscribe(x => console.log(x));
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* ```
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*
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* @see {@link map}
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*
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* @param {any} value The value to map each source value to.
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* @return {Observable} An Observable that emits the given `value` every time
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* the source Observable emits something.
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* @method mapTo
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* @owner Observable
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*/
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export function mapTo<T, R>(value: R): OperatorFunction<T, R> {
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return (source: Observable<T>) => source.lift(new MapToOperator(value));
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}
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class MapToOperator<T, R> implements Operator<T, R> {
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value: R;
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constructor(value: R) {
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this.value = value;
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}
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call(subscriber: Subscriber<R>, source: any): any {
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return source.subscribe(new MapToSubscriber(subscriber, this.value));
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}
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}
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/**
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* We need this JSDoc comment for affecting ESDoc.
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* @ignore
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* @extends {Ignored}
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*/
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class MapToSubscriber<T, R> extends Subscriber<T> {
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value: R;
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constructor(destination: Subscriber<R>, value: R) {
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super(destination);
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this.value = value;
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}
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protected _next(x: T) {
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this.destination.next(this.value);
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}
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}
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