feat(operators): higher-order lettables of reduce, min, max and defaultIfEmpty added

Author: benlesh

src/operator/defaultIfEmpty.ts

@@ -1,6 +1,6 @@
-import { Operator } from '../Operator';
+
 import { Observable } from '../Observable';
-import { Subscriber } from '../Subscriber';
+import { defaultIfEmpty as higherOrder } from '../operators';
 
 /* tslint:disable:max-line-length */
 export function defaultIfEmpty<T>(this: Observable<T>, defaultValue?: T): Observable<T>;
@@ -38,40 +38,5 @@ export function defaultIfEmpty<T, R>(this: Observable<T>, defaultValue?: R): Obs
  * @owner Observable
  */
 export function defaultIfEmpty<T, R>(this: Observable<T>, defaultValue: R = null): Observable<T | R> {
-  return this.lift(new DefaultIfEmptyOperator(defaultValue));
-}
-
-class DefaultIfEmptyOperator<T, R> implements Operator<T, T | R> {
-
-  constructor(private defaultValue: R) {
-  }
-
-  call(subscriber: Subscriber<T | R>, source: any): any {
-    return source.subscribe(new DefaultIfEmptySubscriber(subscriber, this.defaultValue));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class DefaultIfEmptySubscriber<T, R> extends Subscriber<T> {
-  private isEmpty: boolean = true;
-
-  constructor(destination: Subscriber<T | R>, private defaultValue: R) {
-    super(destination);
-  }
-
-  protected _next(value: T): void {
-    this.isEmpty = false;
-    this.destination.next(value);
-  }
-
-  protected _complete(): void {
-    if (this.isEmpty) {
-      this.destination.next(this.defaultValue);
-    }
-    this.destination.complete();
-  }
+  return higherOrder<T, R>(defaultValue)(this);
 }

src/operator/max.ts

@@ -1,5 +1,5 @@
 import { Observable } from '../Observable';
-import { ReduceOperator } from './reduce';
+import { max as higherOrderMax } from '../operators';
 
 /**
  * The Max operator operates on an Observable that emits numbers (or items that can be compared with a provided function),
@@ -33,8 +33,5 @@ import { ReduceOperator } from './reduce';
  * @owner Observable
  */
 export function max<T>(this: Observable<T>, comparer?: (x: T, y: T) => number): Observable<T> {
-  const max: (x: T, y: T) => T = (typeof comparer === 'function')
-    ? (x, y) => comparer(x, y) > 0 ? x : y
-    : (x, y) => x > y ? x : y;
-  return this.lift(new ReduceOperator(max));
+  return higherOrderMax(comparer)(this);
 }

src/operator/min.ts

@@ -1,5 +1,5 @@
 import { Observable } from '../Observable';
-import { ReduceOperator } from './reduce';
+import { min as higherOrderMin } from '../operators';
 
 /**
  * The Min operator operates on an Observable that emits numbers (or items that can be compared with a provided function),
@@ -33,8 +33,5 @@ import { ReduceOperator } from './reduce';
  * @owner Observable
  */
 export function min<T>(this: Observable<T>, comparer?: (x: T, y: T) => number): Observable<T> {
-  const min: (x: T, y: T) => T = (typeof comparer === 'function')
-    ? (x, y) => comparer(x, y) < 0 ? x : y
-    : (x, y) => x < y ? x : y;
-  return this.lift(new ReduceOperator(min));
+  return higherOrderMin(comparer)(this);
 }

src/operator/reduce.ts

@@ -1,6 +1,5 @@
 import { Observable } from '../Observable';
-import { Operator } from '../Operator';
-import { Subscriber } from '../Subscriber';
+import { reduce as higherOrderReduce } from '../operators';
 
 /* tslint:disable:max-line-length */
 export function reduce<T>(this: Observable<T>, accumulator: (acc: T, value: T, index: number) => T, seed?: T): Observable<T>;
@@ -53,73 +52,14 @@ export function reduce<T, R>(this: Observable<T>, accumulator: (acc: R, value: T
  * @owner Observable
  */
 export function reduce<T, R>(this: Observable<T>, accumulator: (acc: R, value: T, index?: number) => R, seed?: R): Observable<R> {
-  let hasSeed = false;
   // providing a seed of `undefined` *should* be valid and trigger
   // hasSeed! so don't use `seed !== undefined` checks!
   // For this reason, we have to check it here at the original call site
   // otherwise inside Operator/Subscriber we won't know if `undefined`
   // means they didn't provide anything or if they literally provided `undefined`
   if (arguments.length >= 2) {
-    hasSeed = true;
+    return higherOrderReduce(accumulator, seed)(this);
   }
 
-  return this.lift(new ReduceOperator(accumulator, seed, hasSeed));
-}
-
-export class ReduceOperator<T, R> implements Operator<T, R> {
-  constructor(private accumulator: (acc: R, value: T, index?: number) => R, private seed?: R, private hasSeed: boolean = false) {}
-
-  call(subscriber: Subscriber<R>, source: any): any {
-    return source.subscribe(new ReduceSubscriber(subscriber, this.accumulator, this.seed, this.hasSeed));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-export class ReduceSubscriber<T, R> extends Subscriber<T> {
-  private index: number = 0;
-  private acc: T | R;
-  private hasValue: boolean = false;
-
-  constructor(destination: Subscriber<R>,
-              private accumulator: (acc: R, value: T, index?: number) => R,
-              seed: R,
-              private hasSeed: boolean) {
-    super(destination);
-    this.acc = seed;
-
-    if (!this.hasSeed) {
-      this.index++;
-    }
-  }
-
-  protected _next(value: T) {
-    if (this.hasValue || (this.hasValue = this.hasSeed)) {
-      this._tryReduce(value);
-    } else {
-      this.acc = value;
-      this.hasValue = true;
-    }
-  }
-
-  private _tryReduce(value: T) {
-    let result: any;
-    try {
-      result = this.accumulator(<R>this.acc, value, this.index++);
-    } catch (err) {
-      this.destination.error(err);
-      return;
-    }
-    this.acc = result;
-  }
-
-  protected _complete() {
-    if (this.hasValue || this.hasSeed) {
-      this.destination.next(this.acc);
-    }
-    this.destination.complete();
-  }
+  return higherOrderReduce(accumulator)(this);
 }

src/operators/defaultIfEmpty.ts

@@ -0,0 +1,80 @@
+import { Operator } from '../Operator';
+import { Observable } from '../Observable';
+import { Subscriber } from '../Subscriber';
+import { OperatorFunction } from '../interfaces';
+
+/* tslint:disable:max-line-length */
+export function defaultIfEmpty<T>(defaultValue?: T): OperatorFunction<T, T>;
+export function defaultIfEmpty<T, R>(defaultValue?: R): OperatorFunction<T, T | R>;
+/* tslint:enable:max-line-length */
+
+/**
+ * Emits a given value if the source Observable completes without emitting any
+ * `next` value, otherwise mirrors the source Observable.
+ *
+ * <span class="informal">If the source Observable turns out to be empty, then
+ * this operator will emit a default value.</span>
+ *
+ * <img src="./img/defaultIfEmpty.png" width="100%">
+ *
+ * `defaultIfEmpty` emits the values emitted by the source Observable or a
+ * specified default value if the source Observable is empty (completes without
+ * having emitted any `next` value).
+ *
+ * @example <caption>If no clicks happen in 5 seconds, then emit "no clicks"</caption>
+ * var clicks = Rx.Observable.fromEvent(document, 'click');
+ * var clicksBeforeFive = clicks.takeUntil(Rx.Observable.interval(5000));
+ * var result = clicksBeforeFive.defaultIfEmpty('no clicks');
+ * result.subscribe(x => console.log(x));
+ *
+ * @see {@link empty}
+ * @see {@link last}
+ *
+ * @param {any} [defaultValue=null] The default value used if the source
+ * Observable is empty.
+ * @return {Observable} An Observable that emits either the specified
+ * `defaultValue` if the source Observable emits no items, or the values emitted
+ * by the source Observable.
+ * @method defaultIfEmpty
+ * @owner Observable
+ */
+export function defaultIfEmpty<T, R>(defaultValue: R = null): OperatorFunction<T, T | R> {
+  return function defaultIfEmptyOperatorFunction(source: Observable<T>) {
+    return source.lift(new DefaultIfEmptyOperator(defaultValue));
+  };
+}
+
+class DefaultIfEmptyOperator<T, R> implements Operator<T, T | R> {
+
+  constructor(private defaultValue: R) {
+  }
+
+  call(subscriber: Subscriber<T | R>, source: any): any {
+    return source.subscribe(new DefaultIfEmptySubscriber(subscriber, this.defaultValue));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class DefaultIfEmptySubscriber<T, R> extends Subscriber<T> {
+  private isEmpty: boolean = true;
+
+  constructor(destination: Subscriber<T | R>, private defaultValue: R) {
+    super(destination);
+  }
+
+  protected _next(value: T): void {
+    this.isEmpty = false;
+    this.destination.next(value);
+  }
+
+  protected _complete(): void {
+    if (this.isEmpty) {
+      this.destination.next(this.defaultValue);
+    }
+    this.destination.complete();
+  }
+}

src/operators/index.ts

@@ -1,7 +1,11 @@
 export { concatMap } from './concatMap';
+export { defaultIfEmpty } from './defaultIfEmpty';
 export { filter } from './filter';
 export { map } from './map';
+export { max } from './max';
 export { mergeMap } from './mergeMap';
+export { min } from './min';
+export { reduce } from './reduce';
 export { scan } from './scan';
 export { switchMap } from './switchMap';
 export { takeLast } from './takeLast';

src/operators/max.ts

@@ -0,0 +1,41 @@
+import { reduce } from './reduce';
+import { OperatorFunction } from '../interfaces';
+
+/**
+ * The Max operator operates on an Observable that emits numbers (or items that can be compared with a provided function),
+ * and when source Observable completes it emits a single item: the item with the largest value.
+ *
+ * <img src="./img/max.png" width="100%">
+ *
+ * @example <caption>Get the maximal value of a series of numbers</caption>
+ * Rx.Observable.of(5, 4, 7, 2, 8)
+ *   .max()
+ *   .subscribe(x => console.log(x)); // -> 8
+ *
+ * @example <caption>Use a comparer function to get the maximal item</caption>
+ * interface Person {
+ *   age: number,
+ *   name: string
+ * }
+ * Observable.of<Person>({age: 7, name: 'Foo'},
+ *                       {age: 5, name: 'Bar'},
+ *                       {age: 9, name: 'Beer'})
+ *           .max<Person>((a: Person, b: Person) => a.age < b.age ? -1 : 1)
+ *           .subscribe((x: Person) => console.log(x.name)); // -> 'Beer'
+ * }
+ *
+ * @see {@link min}
+ *
+ * @param {Function} [comparer] - Optional comparer function that it will use instead of its default to compare the
+ * value of two items.
+ * @return {Observable} An Observable that emits item with the largest value.
+ * @method max
+ * @owner Observable
+ */
+export function max<T>(comparer?: (x: T, y: T) => number): OperatorFunction<T, T> {
+  const max: (x: T, y: T) => T = (typeof comparer === 'function')
+    ? (x, y) => comparer(x, y) > 0 ? x : y
+    : (x, y) => x > y ? x : y;
+
+  return reduce(max);
+}

src/operators/min.ts

@@ -0,0 +1,40 @@
+import { reduce } from './reduce';
+import { OperatorFunction } from '../interfaces';
+
+/**
+ * The Min operator operates on an Observable that emits numbers (or items that can be compared with a provided function),
+ * and when source Observable completes it emits a single item: the item with the smallest value.
+ *
+ * <img src="./img/min.png" width="100%">
+ *
+ * @example <caption>Get the minimal value of a series of numbers</caption>
+ * Rx.Observable.of(5, 4, 7, 2, 8)
+ *   .min()
+ *   .subscribe(x => console.log(x)); // -> 2
+ *
+ * @example <caption>Use a comparer function to get the minimal item</caption>
+ * interface Person {
+ *   age: number,
+ *   name: string
+ * }
+ * Observable.of<Person>({age: 7, name: 'Foo'},
+ *                       {age: 5, name: 'Bar'},
+ *                       {age: 9, name: 'Beer'})
+ *           .min<Person>( (a: Person, b: Person) => a.age < b.age ? -1 : 1)
+ *           .subscribe((x: Person) => console.log(x.name)); // -> 'Bar'
+ * }
+ *
+ * @see {@link max}
+ *
+ * @param {Function} [comparer] - Optional comparer function that it will use instead of its default to compare the
+ * value of two items.
+ * @return {Observable<R>} An Observable that emits item with the smallest value.
+ * @method min
+ * @owner Observable
+ */
+export function min<T>(comparer?: (x: T, y: T) => number): OperatorFunction<T, T> {
+  const min: (x: T, y: T) => T = (typeof comparer === 'function')
+    ? (x, y) => comparer(x, y) < 0 ? x : y
+    : (x, y) => x < y ? x : y;
+  return reduce(min);
+}