Reimplement filter<T>() with native interators

packages/algorithm/src/filter.ts

@@ -7,89 +7,35 @@
 |
 | The full license is in the file LICENSE, distributed with this software.
 |----------------------------------------------------------------------------*/
-import { IIterator, iter, IterableOrArrayLike } from './iter';
 
 /**
  * Filter an iterable for values which pass a test.
  *
- * @param object - The iterable or array-like object of interest.
+ * @param object - The iterable object of interest.
  *
  * @param fn - The predicate function to invoke for each value.
  *
  * @returns An iterator which yields the values which pass the test.
  *
  * #### Example
  * ```typescript
- * import { filter, toArray } from '@lumino/algorithm';
+ * import { filter } from '@lumino/algorithm';
  *
  * let data = [1, 2, 3, 4, 5, 6];
  *
  * let stream = filter(data, value => value % 2 === 0);
  *
- * toArray(stream);  // [2, 4, 6]
+ * Array.from(stream);  // [2, 4, 6]
  * ```
  */
-export function filter<T>(
-  object: IterableOrArrayLike<T>,
+export function* filter<T>(
+  object: Iterable<T>,
   fn: (value: T, index: number) => boolean
-): IIterator<T> {
-  return new FilterIterator<T>(iter(object), fn);
-}
-
-/**
- * An iterator which yields values which pass a test.
- */
-export class FilterIterator<T> implements IIterator<T> {
-  /**
-   * Construct a new filter iterator.
-   *
-   * @param source - The iterator of values of interest.
-   *
-   * @param fn - The predicate function to invoke for each value.
-   */
-  constructor(source: IIterator<T>, fn: (value: T, index: number) => boolean) {
-    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<T> {
-    return this;
-  }
-
-  /**
-   * Create an independent clone of the iterator.
-   *
-   * @returns A new independent clone of the iterator.
-   */
-  clone(): IIterator<T> {
-    let result = new FilterIterator<T>(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(): T | undefined {
-    let fn = this._fn;
-    let it = this._source;
-    let value: T | undefined;
-    while ((value = it.next()) !== undefined) {
-      if (fn(value, this._index++)) {
-        return value;
-      }
+) {
+  const it = object[Symbol.iterator]();
+  for (let index = 0, item = it.next(); !item.done; item = it.next()) {
+    if (fn(item.value, index++)) {
+      yield item.value;
     }
-    return undefined;
   }
-
-  private _index = 0;
-  private _source: IIterator<T>;
-  private _fn: (value: T, index: number) => boolean;
 }