PHP、大型 switch 语句或每次支付数组初始化费用的数组键查找中哪个更快? [英] What's faster in PHP, a big switch statement, or an array key lookup where the array initialisation is paid every time?

问题描述

PHP 中哪个更快，创建一个大的 switch 语句，或者设置一个数组并查找键?

What's faster in PHP, making a large switch statement, or setting up an array and looking up the key?

现在在你回答之前，我很清楚，对于纯查找，数组更快.但是，这是假设只创建一次数组，然后反复查找.

Now before you answer, I am well aware that for pure lookups the array is faster. But, this is assuming creating the array just once, then looking it up repeatedly.

但这不是我正在做的 - 每次运行代码都是新的，并且每次将只使用一次数组.因此，每次都需要重新计算所有数组哈希，我想知道这样做是否比简单地使用 switch 语句慢.

But that's not what I'm doing - each run through the code is new, and the array will be used just once each time. So all the array hashes need to be calculated fresh each time, and I'm wondering if doing that setup is slower than simply having a switch statement.

推荐答案

我做了一些测试:

<?
    echo '<?
        $a = 432;
        $hash = array(
    ';

    for($i = 0; $i < 10000; $i++)
        echo "$i => $i,\n";

    echo ');
        echo $hash[$a];
    ';

文件 switch_gen.php:

<?
    echo '<?
        $a = 432;
        switch($a) {
    ';
    for($i = 0; $i < 10000; $i++)
        echo "case $i: echo $i; break;\n";

    echo '}';

那么:

php array_gen.php > array_.php
php switch_gen.php > switch.php

time tcsh -c 'repeat 1000 php array.php > /dev/null'
19.297u 4.791s 0:25.16 95.7%
time tcsh -c 'repeat 1000 php switch.php > /dev/null'
25.081u 5.543s 0:31.66 96.7%

然后我将循环修改为:

for($i = 'a'; $i < 'z'; $i++)
  for($j = 'a'; $j < 'z'; $j++)
    for($k = 'a'; $k < 'z'; $k++)

要创建 17576 个，3 个字母组合.

To create 17576, 3 letter combinations.

time tcsh -c 'repeat 1000 php array.php > /dev/null'
30.916u 5.831s 0:37.85 97.0%
time tcsh -c 'repeat 1000 php switch.php > /dev/null'
36.257u 6.624s 0:43.96 97.5%

数组方法每次都会获胜，即使包括设置时间也是如此.但不是很多.所以我想我会忽略这个优化并选择更容易的.

The array method wins every time, even once you include setup time. But not by a lot. So I think I will ignore this optimization and go with whatever is easier.

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