Reimplement map<T>() with native interators

packages/algorithm/src/map.ts

@@ -7,85 +7,32 @@
 |
 | The full license is in the file LICENSE, distributed with this software.
 |----------------------------------------------------------------------------*/
-import { IIterator, iter, IterableOrArrayLike } from './iter';
-
 /**
  * Transform the values of an iterable with a mapping function.
  *
- * @param object - The iterable or array-like object of interest.
+ * @param object - The iterable object of interest.
  *
  * @param fn - The mapping function to invoke for each value.
  *
  * @returns An iterator which yields the transformed values.
  *
  * #### Example
  * ```typescript
- * import { map, toArray } from '@lumino/algorithm';
+ * import { map } from '@lumino/algorithm';
  *
  * let data = [1, 2, 3];
  *
  * let stream = map(data, value => value * 2);
  *
- * toArray(stream);  // [2, 4, 6]
+ * Array.from(stream);  // [2, 4, 6]
  * ```
  */
-export function map<T, U>(
-  object: IterableOrArrayLike<T>,
+export function* map<T, U>(
+  object: Iterable<T>,
   fn: (value: T, index: number) => U
-): IIterator<U> {
-  return new MapIterator<T, U>(iter(object), fn);
-}
-
-/**
- * An iterator which transforms values using a mapping function.
- */
-export class MapIterator<T, U> implements IIterator<U> {
-  /**
-   * Construct a new map iterator.
-   *
-   * @param source - The iterator of values of interest.
-   *
-   * @param fn - The mapping function to invoke for each value.
-   */
-  constructor(source: IIterator<T>, fn: (value: T, index: number) => U) {
-    this._source = source;
-    this._fn = fn;
-  }
-
-  /**
-   * Get an iterator over the object's values.
-   *
-   * @returns An iterator which yields the object's values.
-   */
-  iter(): IIterator<U> {
-    return this;
-  }
-
-  /**
-   * Create an independent clone of the iterator.
-   *
-   * @returns A new independent clone of the iterator.
-   */
-  clone(): IIterator<U> {
-    let result = new MapIterator<T, U>(this._source.clone(), this._fn);
-    result._index = this._index;
-    return result;
-  }
-
-  /**
-   * Get the next value from the iterator.
-   *
-   * @returns The next value from the iterator, or `undefined`.
-   */
-  next(): U | undefined {
-    let value = this._source.next();
-    if (value === undefined) {
-      return undefined;
-    }
-    return this._fn.call(undefined, value, this._index++);
+) {
+  let index = 0;
+  for (const value of object) {
+    yield fn(value, index++);
   }
-
-  private _index = 0;
-  private _source: IIterator<T>;
-  private _fn: (value: T, index: number) => U;
 }