iterator_apply()

(PHP 5 >= 5.1.0, PHP 7)

为迭代器中每个元素调用一个用户自定义函数

说明

iterator_apply(Traversable$iterator,callable $function[,array $args]): int

循环迭代每个元素时调用某一回调函数。

参数

$iterator

需要循环迭代的类对象。

$function

迭代到每个元素时的调用的回调函数。

Note:为了遍历$iterator这个函数必须返回TRUE。

$args

传递到回调函数的参数。

返回值

返回已迭代的元素个数。

范例

iterator_apply() example

<?php
function print_caps(Iterator $iterator) {
    echo strtoupper($iterator->current()) . "\n";
    return TRUE;
}
$it = new ArrayIterator(array("Apples", "Bananas", "Cherries"));
iterator_apply($it, "print_caps", array($it));
?>

以上例程会输出：

APPLES
BANANAS
CHERRIES

参见

• array_walk()使用用户自定义函数对数组中的每个元素做回调处理

Each of the arguments required by the function, must be in the array supplied in the third argument to iterator_apply. You can use references too. Example:
<?php
function translate_to(string $target_language, Iterator $words, array $dictionaries) {
  
  $language = ucfirst($target_language);
  $dictionary = $dictionaries[$target_language] ?? 'not found';
  
  if ($dictionary === 'not found') {
    echo "Not found dictionary for {$language}\n";
    return;
  }
  
  echo "English words translated to {$language}\n";
  
  $not_found = [];
  
  iterator_apply($words, function($words, $dictionary, &$not_found){
  
    $english_word = $words->current();
  
    $translated_word = $dictionary[$english_word] ?? '';
  
    if ($translated_word !== '') {
      echo "{$english_word} translates to {$translated_word}\n";
    } else {
      $not_found[] = $english_word;
    }
    return true;
  
  }, array($words, $dictionary, &$not_found));
  
  echo "\nNot found words:\n" . implode("\n", $not_found) . "\n";
}
$dictionaries = [
  'nahuatl' => [
    'one' => 'Ze',
    'two' => 'Ome',
    'three' => 'Yei',
    'four' => 'Nahui',
  ],
];
$iterator = new \ArrayIterator(array('one', 'two', 'three', 'four', 'gasoil'));
translate_to('nahuatl', $iterator, $dictionaries);
?>
English words translated to Nahuatl
one translates to Ze
two translates to Ome
three translates to Yei
four translates to Nahui
Not found words:
gasoil

Be aware of the proper methods to iterate the specific Iterator you are consuming, as the implementation of the method could vary its behaviour.
For example, unlike the ArrayIterator, you can't iterate on a SplDoubleLinkedList with current() without using next() on every iteration (and then, only would iterate if you return true at the end of the callable. It is far easier then with LinkedLists use a while($it->valid()) { $it->current(); $it->next(); }
Let's see:
<?php
$ll = new \SplDoublyLinkedList();
$ll->push('ze');
$ll->push('ome');
$ll->push('yei');
$ll->push('nahui');
$ll->rewind();
$iterations_done = iterator_apply($ll, function(Iterator $it) {
  echo implode("\t=>", [
    $it->key(),
    $it->current(),
    ucfirst($it->current())
  ]),"\n";
  
  return true;
}, array($ll));
echo "Did iterate {$iterations_done} times \n";
$ll->rewind();
$iterations_done = iterator_apply($ll, function(Iterator $it) {
  echo implode("\t=>", [
    $it->key(),
    $it->current(),
    ucfirst($it->current())
  ]),"\n";
  
  $it->next();
  
  return true;
}, array($ll));
echo "Did iterate {$iterations_done} times \n";
$ll->setIteratorMode(SplDoublyLinkedList::IT_MODE_FIFO | SplDoublyLinkedList::IT_MODE_DELETE);
var_dump($ll->count());
foreach($ll as $key => $val) {
  echo "{$key}\t",ucfirst($val),"\n";
}
var_dump($ll->count());
?>
Output:
0  =>ze  =>Ze
0  =>ze  =>Ze
0  =>ze  =>Ze
0  =>ze  =>Ze
Did iterate 4 times 
0  =>ze  =>Ze
1  =>ome  =>Ome
2  =>yei  =>Yei
3  =>nahui  =>Nahui
Did iterate 4 times 
int(4)
0  Ze
0  Ome
0  Yei
0  Nahui
int(0)

$args is an array and each of its elements are passed to the callback as separate arguments.
so this is the right way to get args:
<?php
$ai = new ArrayIterator(range(0, 2));
iterator_apply($ai, function() {
  var_dump(func_get_args());   // use this func
  return true;
}, array(1, 2));
?>
output: 
array(2) {
 [0] =>
 int(1)
 [1] =>
 int(2)
}
array(2) {
 [0] =>
 int(1)
 [1] =>
 int(2)
}
array(2) {
 [0] =>
 int(1)
 [1] =>
 int(2)
}
--------------------------------------------------
or list each args:
<?php
$ai = new ArrayIterator(range(0, 2));
iterator_apply($ai, function($arg1, $arg2, $arg3) {
  var_dump([$arg1, $arg2, $arg3]);
  return true;
}, array(1, 2));
?>
same output.