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feat(single): add higher-order lettable version of single
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3 files changed

+98
-73
lines changed

3 files changed

+98
-73
lines changed

‎src/operator/single.ts‎

Lines changed: 2 additions & 73 deletions
Original file line numberDiff line numberDiff line change
@@ -1,9 +1,5 @@
11
import { Observable } from '../Observable';
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import { Operator } from '../Operator';
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import { Subscriber } from '../Subscriber';
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import { Observer } from '../Observer';
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import { EmptyError } from '../util/EmptyError';
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import { TeardownLogic } from '../Subscription';
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import { single as higherOrder } from '../operators/single';
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/**
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* Returns an Observable that emits the single item emitted by the source Observable that matches a specified
@@ -22,72 +18,5 @@ import { TeardownLogic } from '../Subscription';
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* @owner Observable
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*/
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export function single<T>(this: Observable<T>, predicate?: (value: T, index: number, source: Observable<T>) => boolean): Observable<T> {
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return this.lift(new SingleOperator(predicate, this));
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}
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class SingleOperator<T> implements Operator<T, T> {
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constructor(private predicate?: (value: T, index: number, source: Observable<T>) => boolean,
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private source?: Observable<T>) {
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}
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call(subscriber: Subscriber<T>, source: any): TeardownLogic {
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return source.subscribe(new SingleSubscriber(subscriber, this.predicate, this.source));
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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 SingleSubscriber<T> extends Subscriber<T> {
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private seenValue: boolean = false;
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private singleValue: T;
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private index: number = 0;
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constructor(destination: Observer<T>,
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private predicate?: (value: T, index: number, source: Observable<T>) => boolean,
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private source?: Observable<T>) {
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super(destination);
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}
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private applySingleValue(value: T): void {
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if (this.seenValue) {
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this.destination.error('Sequence contains more than one element');
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} else {
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this.seenValue = true;
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this.singleValue = value;
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}
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}
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protected _next(value: T): void {
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const index = this.index++;
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if (this.predicate) {
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this.tryNext(value, index);
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} else {
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this.applySingleValue(value);
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}
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}
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private tryNext(value: T, index: number): void {
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try {
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if (this.predicate(value, index, this.source)) {
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this.applySingleValue(value);
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}
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} catch (err) {
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this.destination.error(err);
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}
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}
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protected _complete(): void {
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const destination = this.destination;
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if (this.index > 0) {
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destination.next(this.seenValue ? this.singleValue : undefined);
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destination.complete();
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} else {
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destination.error(new EmptyError);
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}
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}
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return higherOrder(predicate)(this);
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}

‎src/operators/index.ts‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -64,6 +64,7 @@ export { scan } from './scan';
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export { sequenceEqual } from './sequenceEqual';
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export { share } from './share';
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export { shareReplay } from './shareReplay';
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export { single } from './single';
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export { subscribeOn } from './subscribeOn';
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export { switchAll } from './switchAll';
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export { switchMap } from './switchMap';

‎src/operators/single.ts‎

Lines changed: 95 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,95 @@
1+
import { Observable } from '../Observable';
2+
import { Operator } from '../Operator';
3+
import { Subscriber } from '../Subscriber';
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import { Observer } from '../Observer';
5+
import { EmptyError } from '../util/EmptyError';
6+
import { TeardownLogic } from '../Subscription';
7+
8+
import { MonoTypeOperatorFunction } from '../interfaces';
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/**
11+
* Returns an Observable that emits the single item emitted by the source Observable that matches a specified
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* predicate, if that Observable emits one such item. If the source Observable emits more than one such item or no
13+
* such items, notify of an IllegalArgumentException or NoSuchElementException respectively.
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*
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* <img src="./img/single.png" width="100%">
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*
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* @throws {EmptyError} Delivers an EmptyError to the Observer's `error`
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* callback if the Observable completes before any `next` notification was sent.
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* @param {Function} predicate - A predicate function to evaluate items emitted by the source Observable.
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* @return {Observable<T>} An Observable that emits the single item emitted by the source Observable that matches
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* the predicate.
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.
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* @method single
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* @owner Observable
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*/
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export function single<T>(predicate?: (value: T, index: number, source: Observable<T>) => boolean): MonoTypeOperatorFunction<T> {
27+
return (source: Observable<T>) => source.lift(new SingleOperator(predicate, source));
28+
}
29+
30+
class SingleOperator<T> implements Operator<T, T> {
31+
constructor(private predicate?: (value: T, index: number, source: Observable<T>) => boolean,
32+
private source?: Observable<T>) {
33+
}
34+
35+
call(subscriber: Subscriber<T>, source: any): TeardownLogic {
36+
return source.subscribe(new SingleSubscriber(subscriber, this.predicate, this.source));
37+
}
38+
}
39+
40+
/**
41+
* We need this JSDoc comment for affecting ESDoc.
42+
* @ignore
43+
* @extends {Ignored}
44+
*/
45+
class SingleSubscriber<T> extends Subscriber<T> {
46+
private seenValue: boolean = false;
47+
private singleValue: T;
48+
private index: number = 0;
49+
50+
constructor(destination: Observer<T>,
51+
private predicate?: (value: T, index: number, source: Observable<T>) => boolean,
52+
private source?: Observable<T>) {
53+
super(destination);
54+
}
55+
56+
private applySingleValue(value: T): void {
57+
if (this.seenValue) {
58+
this.destination.error('Sequence contains more than one element');
59+
} else {
60+
this.seenValue = true;
61+
this.singleValue = value;
62+
}
63+
}
64+
65+
protected _next(value: T): void {
66+
const index = this.index++;
67+
68+
if (this.predicate) {
69+
this.tryNext(value, index);
70+
} else {
71+
this.applySingleValue(value);
72+
}
73+
}
74+
75+
private tryNext(value: T, index: number): void {
76+
try {
77+
if (this.predicate(value, index, this.source)) {
78+
this.applySingleValue(value);
79+
}
80+
} catch (err) {
81+
this.destination.error(err);
82+
}
83+
}
84+
85+
protected _complete(): void {
86+
const destination = this.destination;
87+
88+
if (this.index > 0) {
89+
destination.next(this.seenValue ? this.singleValue : undefined);
90+
destination.complete();
91+
} else {
92+
destination.error(new EmptyError);
93+
}
94+
}
95+
}

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