PHP 自定义迭代器处理关联数组的正确实践

class MyIterator implements Iterator {
  private $items = [];
  private $pointer = 0;

  public function __construct($items) {
    // array_values() 会将所有键转换为数字索引，丢失原始关联键
    $this->items = array_values($items); 
  }

  public function current() {
    return $this->items[$this->pointer];
  }

  public function key() {
    // 始终返回数字指针，而非原始关联键
    return $this->pointer; 
  }

  public function next() {
    $this->pointer++;
  }

  public function rewind() {
    $this->pointer = 0;
  }

  public function valid() {
    return $this->pointer < count($this->items);
  }
}

function printIterable(iterable $myIterable) {
  foreach($myIterable as $itemKey => $itemValue) {
    echo "$itemKey - $itemValue\n";
  }
}

// 使用关联数组进行测试
$iterator = new MyIterator(["a" => 1, "b" => 2, "c" => 3]);
printIterable($iterator);

class MyArrayIterator implements Iterator {
  private $items = [];

  public function __construct(array $items) {
    // 直接存储原始数组，不使用 array_values()
    $this->items = $items;
  }

  public function current(): mixed {
    // 返回内部数组当前指针指向的值
    return current($this->items);
  }

  public function key(): mixed {
    // 返回内部数组当前指针指向的键
    return key($this->items);
  }

  public function next(): void {
    // 移动内部数组指针到下一个元素
    next($this->items);
  }

  public function rewind(): void {
    // 将内部数组指针重置到第一个元素
    reset($this->items);
  }

  public function valid(): bool {
    // 检查内部数组指针是否指向有效元素
    return key($this->items) !== null;
  }
}

// 示例用法
function printIterableWithCorrectKeys(iterable $myIterable) {
  foreach($myIterable as $itemKey => $itemValue) {
    echo "$itemKey - $itemValue\n";
  }
}

echo "--- 解决方案一：利用 PHP 内部数组指针 ---\n";
$iterator1 = new MyArrayIterator(["a" => 1, "b" => 2, "c" => 3]);
printIterableWithCorrectKeys($iterator1);

$iterator2 = new MyArrayIterator([10 => "apple", 20 => "banana"]);
printIterableWithCorrectKeys($iterator2);

class MyExplicitIterator implements Iterator {
  private $items = [];
  private $keys = []; // 存储所有键的列表
  private $pointer = 0; // 指向 $keys 数组的索引

  public function __construct(array $items) {
    $this->items = $items;
    $this->keys = array_keys($items); // 获取所有原始键
  }

  public function current(): mixed {
    // 通过 $pointer 获取当前键，再用键从 $items 获取值
    return $this->items[$this->key()];
  }

  public function key(): mixed {
    // 返回当前 $pointer 指向的键
    return $this->keys[$this->pointer];
  }

  public function next(): void {
    $this->pointer++;
  }

  public function rewind(): void {
    $this->pointer = 0;
  }

  public function valid(): bool {
    // 检查 $pointer 是否在 $keys 数组的有效范围内
    return $this->pointer < count($this->keys);
  }
}

echo "\n--- 解决方案二：显式维护键列表 ---\n";
$iterator3 = new MyExplicitIterator(["apple" => "red", "banana" => "yellow", "grape" => "purple"]);
printIterableWithCorrectKeys($iterator3);

$iterator4 = new MyExplicitIterator([5 => "five", 1 => "one", 3 => "three"]);
printIterableWithCorrectKeys($iterator4);