array_key_last()

(PHP 7 >= 7.3.0)

Gets the last key of an array

说明

array_key_last(array $array): mixed

Get the last key of the given$arraywithout affecting the internal array pointer.

参数

$array

An array.

返回值

Returns the last key of$arrayif the array is not empty;NULLotherwise.

参见

• array_key_first()Gets the first key of an array
• end() 将数组的内部指针指向最后一个单元

For PHP <= 7.3.0 :
if (! function_exists("array_key_last")) {
  function array_key_last($array) {
    if (!is_array($array) || empty($array)) {
      return NULL;
    }
    
    return array_keys($array)[count($array)-1];
  }
}

// if : php ver < 7 
// array_key_last 
$arr = array('1'=>'bear1','2'=>array('22'=>'bear22'),'3'=>'bear3');
echo end(array_keys($arr));
// result : 3

For PHP < 7.3.0 :
Will work for any type of array
<?php
if ( ! function_exists( 'array_key_last' ) ) {
  /**
   * Polyfill for array_key_last() function added in PHP 7.3.
   *
   * Get the last key of the given array without affecting
   * the internal array pointer.
   *
   * @param array $array An array
   *
   * @return mixed The last key of array if the array is not empty; NULL otherwise.
   */
  function array_key_last( $array ) {
    $key = NULL;
    if ( is_array( $array ) ) {
      end( $array );
      $key = key( $array );
    }
    return $key;
  }
}
?>

<?php 
  // PHP >= 7
  function _array_key_last(array $array){
    return (!empty($array)) ? array_keys($array)[count($array)-1] : null;
  }
  var_dump(_array_key_last(['PHP', 'Javascript', 'Python'])); // 2
 ?>

Try to beat this polyfill in terms of performance!
<?php
if( !function_exists('array_key_last') ) {
  function array_key_last(array $array) {
    if( !empty($array) ) return key(array_slice($array, -1, 1, true));
  }
}
// Bonus
if (!function_exists('array_key_first')) {
  function array_key_first(array $arr) {
    foreach($arr as $key => $unused) return $key;
  }
}
?>

For those who loves tested candies;
<?php
function array_key_last(array $array) {
  // 100000 iters: ~0.068 secs
  return key(array_slice($array, -1));
  // 100000 iters: ~0.070 secs
  return key(array_reverse($array));
  // 100000 iters: ~0.088 secs
  return array_keys($array)[count($array) - 1] ?? null;
}
?>

This polyfill works for PHP 5.6+. 
It is a slight modification of "wes at nospam dot example dot org"'s example:
<?php
  if( !function_exists('array_key_first') ) {
    function array_key_first(array $array) {
      if( $array === [] ) { return NULL; }
      foreach($array as $key => $_) { return $key; }
    }
  }
  if( !function_exists('array_key_last') ) {
    function array_key_last(array $array) {
      if( $array === [] ) { return null; }
       
      // the last 2 args to array_slice are crucial
      return array_key_first(array_slice($array, -1, null, true));
    }
  }

Correct polyfill (one that doesn't make copies of arrays, and that doesn't make use of the IAP) is:
<?php
if(!function_exists('array_key_first')){
  function array_key_first(array $array){
    if($array === []){
      return NULL;
    }
    foreach($array as $key => $_) return $key;
  }
}
if(!function_exists('array_key_last')){
  function array_key_last(array $array){
    if($array === []){
      return NULL;
    }
    return array_key_first(array_slice($array, -1));
  }
}
?>