深入理解PHP迭代器与关联数组的键管理

<?php
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
    $this->items = array_values($items);
  }

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

  public function key() {
    return $this->pointer; // 总是返回数字索引
  }

  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);
?>

0 - 1
1 - 2
2 - 3

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

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

  public function current(): mixed {
    // 返回当前元素的值
    return current($this->items);
  }

  public function key(): mixed {
    // 返回当前元素的键
    return key($this->items);
  }

  public function next(): void {
    // 将内部指针向前移动一位
    next($this->items);
  }

  public function rewind(): void {
    // 将内部指针重置到开头
    reset($this->items);
  }

  public function valid(): bool {
    // 检查当前位置是否有效（键不为 null）
    return key($this->items) !== null;
  }
}

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

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

// 也可以用于数字索引数组
echo "\n--- 数字索引数组测试 ---\n";
$iteratorNumeric = new MyArrayIterator([10, 20, 30]);
printIterable($iteratorNumeric);
?>

a - 1
b - 2
c - 3

--- 数字索引数组测试 ---
0 - 10
1 - 20
2 - 30

<?php
class MyExplicitKeyIterator implements Iterator {
  private $items = [];
  private $keys = []; // 存储原始键的列表
  private $pointer = 0; // 内部数字指针，用于索引 $keys 数组

  public function __construct(array $items) {
    $this->items = $items; // 存储原始数组
    $this->keys = array_keys($items); // 提取所有键
  }

  public function current(): mixed {
    // 使用当前指针从 $keys 数组中获取实际的键，再用这个键从 $items 中获取值
    return $this->items[$this->key()];
  }

  public function key(): mixed {
    // 返回当前指针对应的实际键
    return $this->keys[$this->pointer];
  }

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

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

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

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

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

// 也可以用于数字索引数组
echo "\n--- 数字索引数组测试 ---\n";
$iteratorNumeric = new MyExplicitKeyIterator([10, 20, 30]);
printIterable($iteratorNumeric);
?>

a - 1
b - 2
c - 3

--- 数字索引数组测试 ---
0 - 10
1 - 20
2 - 30