在PHP，大的switch语句或每次都要进行数组初始化的数组键查找中，更快的是什么? [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，执行大型switch语句或设置数组并查找键的速度更快?

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

现在，在您回答之前，我很清楚，对于纯查找而言，数组会更快.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.

但这不是我在做什么-每次运行代码都是新的，并且每次 仅一次 使用该数组.因此，每次都需要重新计算所有数组散列，我想知道这样做是否比仅使用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 '}';

然后:

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个字母的组合.

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%

即使每次包含设置时间，数组方法也会每次都获胜.但不是很多.因此，我认为我将忽略此优化，而选择更容易的方法.

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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