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import { distinctUntilChanged } from './distinctUntilChanged';
import { MonoTypeOperatorFunction } from '../types';
/* tslint:disable:max-line-length */
export function distinctUntilKeyChanged<T>(key: keyof T): MonoTypeOperatorFunction<T>;
export function distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare: (x: T[K], y: T[K]) => boolean): 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,
* using a property accessed by using the key provided to check if the two items are distinct.
*
* 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.
*
* ## Examples
* An example comparing the name of persons
* ```typescript
* import { of } from 'rxjs';
* import { distinctUntilKeyChanged } from 'rxjs/operators';
*
* interface Person {
* age: number,
* name: string
* }
*
*of(
* { age: 4, name: 'Foo'},
* { age: 7, name: 'Bar'},
* { age: 5, name: 'Foo'},
* { age: 6, name: 'Foo'},
* ).pipe(
* distinctUntilKeyChanged('name'),
* )
* .subscribe(x => console.log(x));
*
* // displays:
* // { age: 4, name: 'Foo' }
* // { age: 7, name: 'Bar' }
* // { age: 5, name: 'Foo' }
* ```
*
* An example comparing the first letters of the name
* ```typescript
* import { of } from 'rxjs';
* import { distinctUntilKeyChanged } from 'rxjs/operators';
*
* interface Person {
* age: number,
* name: string
* }
*
*of(
* { age: 4, name: 'Foo1'},
* { age: 7, name: 'Bar'},
* { age: 5, name: 'Foo2'},
* { age: 6, name: 'Foo3'},
* ).pipe(
* distinctUntilKeyChanged('name', (x: string, y: string) => x.substring(0, 3) === y.substring(0, 3)),
* )
* .subscribe(x => console.log(x));
*
* // displays:
* // { age: 4, name: 'Foo1' }
* // { age: 7, name: 'Bar' }
* // { age: 5, name: 'Foo2' }
* ```
*
* @see {@link distinct}
* @see {@link distinctUntilChanged}
*
* @param {string} key String key for object property lookup on each item.
* @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 based on the key specified.
* @method distinctUntilKeyChanged
* @owner Observable
*/
export function distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare?: (x: T[K], y: T[K]) => boolean): MonoTypeOperatorFunction<T> {
return distinctUntilChanged((x: T, y: T) => compare ? compare(x[key], y[key]) : x[key] === y[key]);
}
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