1 | // Copyright (c) Jupyter Development Team.
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2 | // Distributed under the terms of the Modified BSD License.
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3 | /*-----------------------------------------------------------------------------
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4 | | Copyright (c) 2014-2017, PhosphorJS Contributors
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5 | |
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6 | | Distributed under the terms of the BSD 3-Clause License.
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7 | |
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8 | | The full license is in the file LICENSE, distributed with this software.
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9 | |----------------------------------------------------------------------------*/
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10 | import { IIterator } from './iter';
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11 |
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12 | /**
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13 | * Create an empty iterator.
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14 | *
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15 | * @returns A new iterator which yields nothing.
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16 | *
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17 | * #### Example
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18 | * ```typescript
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19 | * import { empty, toArray } from '@lumino/algorithm';
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20 | *
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21 | * let stream = empty<number>();
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22 | *
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23 | * toArray(stream); // []
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24 | * ```
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25 | */
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26 | export function empty<T>(): IIterator<T> {
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27 | return new EmptyIterator<T>();
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28 | }
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29 |
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30 | /**
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31 | * An iterator which is always empty.
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32 | */
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33 | export class EmptyIterator<T> implements IIterator<T> {
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34 | /**
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35 | * Get an iterator over the object's values.
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36 | *
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37 | * @returns An iterator which yields the object's values.
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38 | */
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39 | iter(): IIterator<T> {
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40 | return this;
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41 | }
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42 |
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43 | /**
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44 | * Create an independent clone of the iterator.
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45 | *
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46 | * @returns A new independent clone of the iterator.
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47 | */
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48 | clone(): IIterator<T> {
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49 | return new EmptyIterator<T>();
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50 | }
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51 |
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52 | /**
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53 | * Get the next value from the iterator.
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54 | *
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55 | * @returns The next value from the iterator, or `undefined`.
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56 | */
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57 | next(): T | undefined {
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58 | return undefined;
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59 | }
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60 | }
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