feat(distinct): add higher-order lettable version of distinct

src/operator/distinct.ts

@@ -1,11 +1,5 @@
 import { Observable } from '../Observable';
-import { Operator } from '../Operator';
-import { Subscriber } from '../Subscriber';
-import { TeardownLogic } from '../Subscription';
-import { OuterSubscriber } from '../OuterSubscriber';
-import { InnerSubscriber } from '../InnerSubscriber';
-import { subscribeToResult } from '../util/subscribeToResult';
-import { ISet, Set } from '../util/Set';
+import { distinct as higherOrder } from '../operators';
 
 /**
  * Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from previous items.
@@ -55,70 +49,5 @@ import { ISet, Set } from '../util/Set';
 export function distinct<T, K>(this: Observable<T>,
                                keySelector?: (value: T) => K,
                                flushes?: Observable<any>): Observable<T> {
-  return this.lift(new DistinctOperator(keySelector, flushes));
-}
-
-class DistinctOperator<T, K> implements Operator<T, T> {
-  constructor(private keySelector: (value: T) => K, private flushes: Observable<any>) {
-  }
-
-  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
-    return source.subscribe(new DistinctSubscriber(subscriber, this.keySelector, this.flushes));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-export class DistinctSubscriber<T, K> extends OuterSubscriber<T, T> {
-  private values: ISet<K> = new Set<K>();
-
-  constructor(destination: Subscriber<T>, private keySelector: (value: T) => K, flushes: Observable<any>) {
-    super(destination);
-
-    if (flushes) {
-      this.add(subscribeToResult(this, flushes));
-    }
-  }
-
-  notifyNext(outerValue: T, innerValue: T,
-             outerIndex: number, innerIndex: number,
-             innerSub: InnerSubscriber<T, T>): void {
-    this.values.clear();
-  }
-
-  notifyError(error: any, innerSub: InnerSubscriber<T, T>): void {
-    this._error(error);
-  }
-
-  protected _next(value: T): void {
-    if (this.keySelector) {
-      this._useKeySelector(value);
-    } else {
-      this._finalizeNext(value, value);
-    }
-  }
-
-  private _useKeySelector(value: T): void {
-    let key: K;
-    const { destination } = this;
-    try {
-      key = this.keySelector(value);
-    } catch (err) {
-      destination.error(err);
-      return;
-    }
-    this._finalizeNext(key, value);
-  }
-
-  private _finalizeNext(key: K|T, value: T) {
-    const { values } = this;
-    if (!values.has(<K>key)) {
-      values.add(<K>key);
-      this.destination.next(value);
-    }
-  }
-
+  return higherOrder(keySelector, flushes)(this);
 }

src/operators/distinct.ts

@@ -0,0 +1,124 @@
+import { Observable } from '../Observable';
+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { TeardownLogic } from '../Subscription';
+import { OuterSubscriber } from '../OuterSubscriber';
+import { InnerSubscriber } from '../InnerSubscriber';
+import { subscribeToResult } from '../util/subscribeToResult';
+import { ISet, Set } from '../util/Set';
+import { MonoTypeOperatorFunction } from '../interfaces';
+
+/**
+ * Returns an Observable that emits all items emitted by the source Observable that are distinct by comparison from previous items.
+ *
+ * If a keySelector function is provided, then it will project each value from the source observable into a new value that it will
+ * check for equality with previously projected values. If a keySelector function is not provided, it will use each value from the
+ * source observable directly with an equality check against previous values.
+ *
+ * In JavaScript runtimes that support `Set`, this operator will use a `Set` to improve performance of the distinct value checking.
+ *
+ * In other runtimes, this operator will use a minimal implementation of `Set` that relies on an `Array` and `indexOf` under the
+ * hood, so performance will degrade as more values are checked for distinction. Even in newer browsers, a long-running `distinct`
+ * use might result in memory leaks. To help alleviate this in some scenarios, an optional `flushes` parameter is also provided so
+ * that the internal `Set` can be "flushed", basically clearing it of values.
+ *
+ * @example <caption>A simple example with numbers</caption>
+ * Observable.of(1, 1, 2, 2, 2, 1, 2, 3, 4, 3, 2, 1)
+ *   .distinct()
+ *   .subscribe(x => console.log(x)); // 1, 2, 3, 4
+ *
+ * @example <caption>An example using a keySelector function</caption>
+ * interface Person {
+ *    age: number,
+ *    name: string
+ * }
+ *
+ * Observable.of<Person>(
+ *     { age: 4, name: 'Foo'},
+ *     { age: 7, name: 'Bar'},
+ *     { age: 5, name: 'Foo'})
+ *     .distinct((p: Person) => p.name)
+ *     .subscribe(x => console.log(x));
+ *
+ * // displays:
+ * // { age: 4, name: 'Foo' }
+ * // { age: 7, name: 'Bar' }
+ *
+ * @see {@link distinctUntilChanged}
+ * @see {@link distinctUntilKeyChanged}
+ *
+ * @param {function} [keySelector] Optional function to select which value you want to check as distinct.
+ * @param {Observable} [flushes] Optional Observable for flushing the internal HashSet of the operator.
+ * @return {Observable} An Observable that emits items from the source Observable with distinct values.
+ * @method distinct
+ * @owner Observable
+ */
+export function distinct<T, K>(keySelector?: (value: T) => K,
+                               flushes?: Observable<any>): MonoTypeOperatorFunction<T> {
+  return (source: Observable<T>) => source.lift(new DistinctOperator(keySelector, flushes));
+}
+
+class DistinctOperator<T, K> implements Operator<T, T> {
+  constructor(private keySelector: (value: T) => K, private flushes: Observable<any>) {
+  }
+
+  call(subscriber: Subscriber<T>, source: any): TeardownLogic {
+    return source.subscribe(new DistinctSubscriber(subscriber, this.keySelector, this.flushes));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+export class DistinctSubscriber<T, K> extends OuterSubscriber<T, T> {
+  private values: ISet<K> = new Set<K>();
+
+  constructor(destination: Subscriber<T>, private keySelector: (value: T) => K, flushes: Observable<any>) {
+    super(destination);
+
+    if (flushes) {
+      this.add(subscribeToResult(this, flushes));
+    }
+  }
+
+  notifyNext(outerValue: T, innerValue: T,
+             outerIndex: number, innerIndex: number,
+             innerSub: InnerSubscriber<T, T>): void {
+    this.values.clear();
+  }
+
+  notifyError(error: any, innerSub: InnerSubscriber<T, T>): void {
+    this._error(error);
+  }
+
+  protected _next(value: T): void {
+    if (this.keySelector) {
+      this._useKeySelector(value);
+    } else {
+      this._finalizeNext(value, value);
+    }
+  }
+
+  private _useKeySelector(value: T): void {
+    let key: K;
+    const { destination } = this;
+    try {
+      key = this.keySelector(value);
+    } catch (err) {
+      destination.error(err);
+      return;
+    }
+    this._finalizeNext(key, value);
+  }
+
+  private _finalizeNext(key: K|T, value: T) {
+    const { values } = this;
+    if (!values.has(<K>key)) {
+      values.add(<K>key);
+      this.destination.next(value);
+    }
+  }
+
+}

src/operators/index.ts

@@ -19,6 +19,7 @@ export { defaultIfEmpty } from './defaultIfEmpty';
 export { delay } from './delay';
 export { delayWhen } from './delayWhen';
 export { dematerialize } from './dematerialize';
+export { distinct } from './distinct';
 export { distinctUntilChanged } from './distinctUntilChanged';
 export { distinctUntilKeyChanged } from './distinctUntilKeyChanged';
 export { elementAt } from './elementAt';