PHP 变量引用和内存使用

2022-01-05 00:00:00 reference variables memory-management php

根据php手册:

<?php
$a =& $b;
?>
// Note:
// $a and $b are completely equal here. $a is not pointing to $b or vice versa.
// $a and $b are pointing to the same place.

我假设:

<?php
$x = "something";
$y = $x;
$z = $x;

应该消耗更多的内存:

<?php
$x = "something";
$y =& $x;
$z =& $x;

因为，如果我理解正确的话，在第一种情况下，我们复制"值 something 并将其分配给 $y 和 $z 最后有 3 个变量和 3 个内容，而在第二种情况下，我们有 3 个变量指向相同的内容.

because, if i understood it right, in the first case we 'duplicate' the value something and assign it to $y and $z having in the end 3 variables and 3 contents, while in the second case we have 3 variables pointing the same content.

所以，使用如下代码:

$value = "put something here, like a long lorem ipsum";
for($i = 0; $i < 100000; $i++)
{
    ${"a$i"} =& $value;
}
echo memory_get_usage(true);

我希望内存使用量低于:

I expect to have a memory usage lower than:

$value = "put something here, like a long lorem ipsum";
for($i = 0; $i < 100000; $i++)
{
    ${"a$i"} = $value;
}
echo memory_get_usage(true);

但是两种情况下的内存使用量是一样的.

But the memory usage is the same in both cases.

我错过了什么?

推荐答案

PHP 不会在赋值时重复，而是在写入时重复.请参阅 PHP 语言中的写时复制(2009 年 1 月 18 日；作者:Akihiko Tozawa、Michiaki Tatsubori、Tamiya Onodera 和 Yasuhiko Minamide；PDF 文件) 对其进行科学讨论，不要使用 PHP 引用(2010 年 1 月 10 日；作者 Jan Schlüter) 一些乐趣，我自己的看法是 参考 Max 以及更多参考.

PHP does not duplicate on assignment, but on write. See Copy-on-Write in the PHP Language (Jan 18 2009; by Akihiko Tozawa, Michiaki Tatsubori, Tamiya Onodera and Yasuhiko Minamide; PDF file) for a scientific discussion of it, Do not use PHP references (Jan 10, 2010; by Jan Schlüter) for some fun and my own take is References to the Max with more references.

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