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@benlesh @Daschyppoo @jasonaden @JWO719 @sulco @moniuch @BioPhoton @bmeurer
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import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
import { Observable } from '../Observable';
import { MonoTypeOperatorFunction, TeardownLogic } from '../types';
/* tslint:disable:max-line-length */
export function distinctUntilChanged<T>(compare?: (x: T, y: T) => boolean): MonoTypeOperatorFunction<T>;
export function distinctUntilChanged<T, K>(compare: (x: K, y: K) => boolean, keySelector: (x: T) => K): MonoTypeOperatorFunction<T>;
/* tslint:enable:max-line-length */
/**
* Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from the previous item.
*
* If a comparator function is provided, then it will be called for each item to test for whether or not that value should be emitted.
*
* If a comparator function is not provided, an equality check is used by default.
*
* ## Example
* A simple example with numbers
* ```ts
* import { of } from 'rxjs';
* import { distinctUntilChanged } from 'rxjs/operators';
*
* of(1, 1, 2, 2, 2, 1, 1, 2, 3, 3, 4).pipe(
* distinctUntilChanged(),
* )
* .subscribe(x => console.log(x)); // 1, 2, 1, 2, 3, 4
* ```
*
* An example using a compare function
* ```typescript
* import { of } from 'rxjs';
* import { distinctUntilChanged } from 'rxjs/operators';
*
* interface Person {
* age: number,
* name: string
* }
*
* of<Person>(
* { age: 4, name: 'Foo'},
* { age: 7, name: 'Bar'},
* { age: 5, name: 'Foo'},
* { age: 6, name: 'Foo'},
* ).pipe(
* distinctUntilChanged((p: Person, q: Person) => p.name === q.name),
* )
* .subscribe(x => console.log(x));
*
* // displays:
* // { age: 4, name: 'Foo' }
* // { age: 7, name: 'Bar' }
* // { age: 5, name: 'Foo' }
* ```
*
* @see {@link distinct}
* @see {@link distinctUntilKeyChanged}
*
* @param {function} [compare] Optional comparison function called to test if an item is distinct from the previous item in the source.
* @return {Observable} An Observable that emits items from the source Observable with distinct values.
* @method distinctUntilChanged
* @owner Observable
*/
export function distinctUntilChanged<T, K>(compare?: (x: K, y: K) => boolean, keySelector?: (x: T) => K): MonoTypeOperatorFunction<T> {
return (source: Observable<T>) => source.lift(new DistinctUntilChangedOperator<T, K>(compare, keySelector));
}
class DistinctUntilChangedOperator<T, K> implements Operator<T, T> {
constructor(private compare: (x: K, y: K) => boolean,
private keySelector: (x: T) => K) {
}
call(subscriber: Subscriber<T>, source: any): TeardownLogic {
return source.subscribe(new DistinctUntilChangedSubscriber(subscriber, this.compare, this.keySelector));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class DistinctUntilChangedSubscriber<T, K> extends Subscriber<T> {
private key: K;
private hasKey: boolean = false;
constructor(destination: Subscriber<T>,
compare: (x: K, y: K) => boolean,
private keySelector: (x: T) => K) {
super(destination);
if (typeof compare === 'function') {
this.compare = compare;
}
}
private compare(x: any, y: any): boolean {
return x === y;
}
protected _next(value: T): void {
let key: any;
try {
const { keySelector } = this;
key = keySelector ? keySelector(value) : value;
} catch (err) {
return this.destination.error(err);
}
let result = false;
if (this.hasKey) {
try {
const { compare } = this;
result = compare(this.key, key);
} catch (err) {
return this.destination.error(err);
}
} else {
this.hasKey = true;
}
if (!result) {
this.key = key;
this.destination.next(value);
}
}
}
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