PHP引用数组的深层副本 [英] Deep copy of PHP array of references

问题描述

所以$ array是一个数组，其中所有元素都是引用.

So $array is an array of which all elements are references.

我想将此数组追加到另一个名为$ results的数组中(循环)，但是由于它们是引用，因此PHP复制了引用，而$ results充满了相同的元素.

I want to append this array to another array called $results (in a loop), but since they are references, PHP copies the references and $results is full of identical elements.

到目前为止，最佳的解决方案是:

So far, the best working solution is:

$results[] = unserialize(serialize($array));

我担心效率低下.有更好的方法吗?

which I fear to be incredibly inefficient. Is there a better way to do this?

推荐答案

您可以使用以下事实:函数在返回时会取消引用结果，例如，此处$array_by_myclone仍将引用$original($array_by_myclone[0][0] == 'foo')，而$array_by_assignment将具有克隆值($array_by_assignment[0][0] == 'bar')

You can use the fact that functions dereferences results when returning, for exemple here $array_by_myclone will still have a reference to $original ($array_by_myclone[0][0] == 'foo') while $array_by_assignment will have a cloned value ($array_by_assignment[0][0] == 'bar')

$original = 'foo';
$array_of_reference = array(&$original);

function myclone($value)
{
  return $value;
}

$array_by_myclone = array();
$array_by_myclone[] = array_map('myclone', $array_of_reference);

$array_by_assignment = array();
$array_by_assignment[] = $array_of_reference;

$original = 'bar';

var_dump($array_by_myclone[0][0]); // foo, values were cloned                                                                                                                                   
var_dump($array_by_assignment[0][0]); // bar, still a reference                     

我想检查说unserialize(serialize())更快的注释是否正确，所以我使用php 5.5进行了测试，事实证明这是错误的:即使在数据集较小的情况下，使用序列化方法也较慢，并且您拥有的数据越多，获取速度就越慢.

I wanted to check if the comment saying unserialize(serialize()) was faster was right so I did the test using php 5.5, and it turns out this is wrong: using the serialization method is slower even with a small dataset, and the more data you have the slower it gets.

lepidosteus@server:~$ php -v
PHP 5.5.1-1~dotdeb.1 (cli) (built: Aug  3 2013 22:19:30) 
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2013 Zend Technologies
    with Zend OPcache v7.0.2-dev, Copyright (c) 1999-2013, by Zend Technologies
lepidosteus@server:~$ php reference.php 1
myclone:   0.000010 seconds
serialize: 0.000012 seconds
lepidosteus@server:~$ php reference.php 1000000
myclone:   0.398540 seconds
serialize: 0.706631 seconds

使用的代码:

<?php
$iterations = 1000000;
if (isset($argv[1]) && is_numeric($argv[1])) {
  $iterations = max(1, (int)$argv[1]);
}

$items = array();
for ($i = 0; $i < $iterations; $i++) {
  $items[] = 'item number '.$i;
}

$array_of_refs = array();
foreach ($items as $k => $v) {
  $array_of_refs[] = &$items[$k];
}

function myclone($value)
{
  return $value;
}

$start = microtime(true);

$copy = array_map('myclone', $array_of_refs);

$time = microtime(true) - $start;

printf("%-10s %2.6f seconds\n", 'myclone:', $time);

$start = microtime(true);

$copy = unserialize(serialize($array_of_refs));

$time = microtime(true) - $start;

printf("%-10s %2.6f seconds\n", 'serialize:', $time);

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