Вы захотите использовать длину контента (URLConnection.getContentLength ()). К сожалению, это не всегда точно, или не всегда может быть предоставлено, поэтому не всегда безопасно полагаться на это.
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($array_by_assignment[0][0]); // bar, still a reference
EDIT: I wanted to check if the comment saying unserialize(serialize())
was faster was right so I did the test using php 5.5, and it turns out this is wrong: using the serialization method is slower even with a small dataset, and the more data you have the slower it gets.
lepidosteus@server:~$ 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
Code used:
<?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);