added MemoizingIterator [WIP]

src/Iterators/MemoizingIterator.php

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+<?php
+
+/**
+ * This file is part of the Nette Framework (https://nette.org)
+ * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
+ */
+
+declare(strict_types=1);
+
+namespace Nette\Iterators;
+
+
+/**
+ * MemoizingIterator wraps around another iterator and caches its keys and values during iteration.
+ * This allows the data to be re-iterated multiple times.
+ * @template K
+ * @template V
+ * @implements \Iterator<K, V>
+ */
+class MemoizingIterator implements \Iterator
+{
+	private array $cache = [];
+	private int $index = 0;
+
+
+	/**
+	 * @param  \Iterator<K, V>  $inner
+	 */
+	public function __construct(
+		private readonly \Iterator $inner,
+	) {
+	}
+
+
+	public function rewind(): void
+	{
+		if (!$this->cache) {
+			$this->inner->rewind();
+		}
+		$this->index = 0;
+	}
+
+
+	/**
+	 * @return V
+	 */
+	public function current(): mixed
+	{
+		return $this->cache[$this->index][1] ?? null;
+	}
+
+
+	/**
+	 * @return K
+	 */
+	public function key(): mixed
+	{
+		return $this->cache[$this->index][0] ?? null;
+	}
+
+
+	public function next(): void
+	{
+		if (!isset($this->cache[++$this->index])) {
+			$this->inner->next();
+		}
+	}
+
+
+	public function valid(): bool
+	{
+		if (!isset($this->cache[$this->index]) && $this->inner->valid()) {
+			$this->cache[$this->index] = [$this->inner->key(), $this->inner->current()];
+		}
+		return isset($this->cache[$this->index]);
+	}
+}

tests/Iterators/MemoizingIterator.phpt

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+<?php
+
+/**
+ * Test: Nette\Iterators\MemoizingIterator
+ */
+
+declare(strict_types=1);
+
+use Nette\Iterators\MemoizingIterator;
+use Tester\Assert;
+
+require __DIR__ . '/../bootstrap.php';
+
+
+function iterator(): Generator
+{
+	yield 'a' => 'apple';
+	yield ['b'] => ['banana'];
+	yield 'c' => 'cherry';
+}
+
+
+test('iteration', function () {
+	$iterator = new MemoizingIterator(iterator());
+
+	$pairs = [];
+	foreach ($iterator as $key => $value) {
+		$pairs[] = [$key, $value];
+	}
+	Assert::same(
+		[
+			['a', 'apple'],
+			[['b'], ['banana']],
+			['c', 'cherry'],
+		],
+		$pairs,
+	);
+});
+
+
+test('re-iteration', function () {
+	$iterator = new MemoizingIterator(iterator());
+
+	foreach ($iterator as $value);
+
+	$pairs = [];
+	foreach ($iterator as $key => $value) {
+		$pairs[] = [$key, $value];
+	}
+	Assert::same(
+		[
+			['a', 'apple'],
+			[['b'], ['banana']],
+			['c', 'cherry'],
+		],
+		$pairs,
+	);
+});
+
+
+test('nested re-iteration', function () { // nefunguje
+	$iterator = new MemoizingIterator(iterator());
+
+	$pairs = [];
+	foreach ($iterator as $key => $value) {
+		$pairs[] = [$key, $value];
+		foreach ($iterator as $value);
+	}
+	Assert::same(
+		[
+			['a', 'apple'],
+			[['b'], ['banana']],
+			['c', 'cherry'],
+		],
+		$pairs,
+	);
+});