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iterator.ts
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iterator.ts
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/*---------------------------------------------------------------------------------------------
* Copyright (c) Microsoft Corporation. All rights reserved.
* Licensed under the MIT License. See License.txt in the project root for license information.
*--------------------------------------------------------------------------------------------*/
export namespace Iterable {
export function is<T = any>(thing: any): thing is Iterable<T> {
return thing && typeof thing === 'object' && typeof thing[Symbol.iterator] === 'function';
}
const _empty: Iterable<any> = Object.freeze([]);
export function empty<T = any>(): Iterable<T> {
return _empty;
}
export function* single<T>(element: T): Iterable<T> {
yield element;
}
export function from<T>(iterable: Iterable<T> | undefined | null): Iterable<T> {
return iterable || _empty;
}
export function isEmpty<T>(iterable: Iterable<T> | undefined | null): boolean {
return !iterable || iterable[Symbol.iterator]().next().done === true;
}
export function first<T>(iterable: Iterable<T>): T | undefined {
return iterable[Symbol.iterator]().next().value;
}
export function some<T>(iterable: Iterable<T>, predicate: (t: T) => unknown): boolean {
for (const element of iterable) {
if (predicate(element)) {
return true;
}
}
return false;
}
export function find<T, R extends T>(iterable: Iterable<T>, predicate: (t: T) => t is R): T | undefined;
export function find<T>(iterable: Iterable<T>, predicate: (t: T) => boolean): T | undefined;
export function find<T>(iterable: Iterable<T>, predicate: (t: T) => boolean): T | undefined {
for (const element of iterable) {
if (predicate(element)) {
return element;
}
}
return undefined;
}
export function filter<T, R extends T>(iterable: Iterable<T>, predicate: (t: T) => t is R): Iterable<R>;
export function filter<T>(iterable: Iterable<T>, predicate: (t: T) => boolean): Iterable<T>;
export function* filter<T>(iterable: Iterable<T>, predicate: (t: T) => boolean): Iterable<T> {
for (const element of iterable) {
if (predicate(element)) {
yield element;
}
}
}
export function* map<T, R>(iterable: Iterable<T>, fn: (t: T, index: number) => R): Iterable<R> {
let index = 0;
for (const element of iterable) {
yield fn(element, index++);
}
}
export function* concat<T>(...iterables: Iterable<T>[]): Iterable<T> {
for (const iterable of iterables) {
for (const element of iterable) {
yield element;
}
}
}
export function* concatNested<T>(iterables: Iterable<Iterable<T>>): Iterable<T> {
for (const iterable of iterables) {
for (const element of iterable) {
yield element;
}
}
}
export function reduce<T, R>(iterable: Iterable<T>, reducer: (previousValue: R, currentValue: T) => R, initialValue: R): R {
let value = initialValue;
for (const element of iterable) {
value = reducer(value, element);
}
return value;
}
export function forEach<T>(iterable: Iterable<T>, fn: (t: T, index: number) => any): void {
let index = 0;
for (const element of iterable) {
fn(element, index++);
}
}
/**
* Returns an iterable slice of the array, with the same semantics as `array.slice()`.
*/
export function* slice<T>(arr: ReadonlyArray<T>, from: number, to = arr.length): Iterable<T> {
if (from < 0) {
from += arr.length;
}
if (to < 0) {
to += arr.length;
} else if (to > arr.length) {
to = arr.length;
}
for (; from < to; from++) {
yield arr[from];
}
}
/**
* Consumes `atMost` elements from iterable and returns the consumed elements,
* and an iterable for the rest of the elements.
*/
export function consume<T>(iterable: Iterable<T>, atMost: number = Number.POSITIVE_INFINITY): [T[], Iterable<T>] {
const consumed: T[] = [];
if (atMost === 0) {
return [consumed, iterable];
}
const iterator = iterable[Symbol.iterator]();
for (let i = 0; i < atMost; i++) {
const next = iterator.next();
if (next.done) {
return [consumed, Iterable.empty()];
}
consumed.push(next.value);
}
return [consumed, { [Symbol.iterator]() { return iterator; } }];
}
/**
* Consumes `atMost` elements from iterable and returns the consumed elements,
* and an iterable for the rest of the elements.
*/
export function collect<T>(iterable: Iterable<T>): T[] {
return consume(iterable)[0];
}
/**
* Returns whether the iterables are the same length and all items are
* equal using the comparator function.
*/
export function equals<T>(a: Iterable<T>, b: Iterable<T>, comparator = (at: T, bt: T) => at === bt) {
const ai = a[Symbol.iterator]();
const bi = b[Symbol.iterator]();
while (true) {
const an = ai.next();
const bn = bi.next();
if (an.done !== bn.done) {
return false;
} else if (an.done) {
return true;
} else if (!comparator(an.value, bn.value)) {
return false;
}
}
}
}