为什么PHP中的转换和比较比is_*更快？

Question

在PHP中优化函数时,我改变了

if(is_array($obj)) foreach($obj as $key=>$value { [snip] } 
else if(is_object($obj)) foreach($obj as $key=>$value { [snip] } 

至

if($obj == (array) $obj) foreach($obj as $key=>$value { [snip] } 
else if($obj == (obj) $obj) foreach($obj as $key=>$value { [snip] } 

在了解之后===,我改变了

if($obj === (array) $obj) foreach($obj as $key=>$value { [snip] } 
else if($obj === (obj) $obj) foreach($obj as $key=>$value { [snip] } 

将每个测试从is_*更改为cast,导致主要加速(> 30%).

我明白这===比==没有强制要求更快,但为什么变量比调用任何_* - 函数快得多？

编辑: 由于每个人都在询问正确性,我写了这个小测试:

$foo=(object) array('bar'=>'foo');
$bar=array('bar'=>'foo');

if($foo===(array) $foo) echo '$foo is an array?';
if($bar===(object) $bar) echo '$bar is an object?';

它没有打印任何错误,并且两个变量都没有改变,所以我认为它有效,但我已经准备好了.

另一个编辑: Artefacto的程序给了我以下数字:

PHP 5.3.2-1ubuntu4.2 (64bit) on a Core i5-750 with Xdebug
Elapsed (1): 0.46174287796021 / 0.28902506828308
Elapsed (2): 0.52625703811646 / 0.3072669506073
Elapsed (3): 0.57169318199158 / 0.12708187103271
Elapsed (4): 0.51496887207031 / 0.30524897575378
Speculation: Casting and comparing can be about 1.7-4 times faster.

PHP 5.3.2-1ubuntu4.2 (64bit) on a Core i5-750 without Xdebug
Elapsed (1): 0.15818405151367 / 0.214271068573
Elapsed (2): 0.1531388759613 / 0.25853085517883
Elapsed (3): 0.16164898872375 / 0.074632883071899
Elapsed (4): 0.14408397674561 / 0.25812387466431
Without Xdebug, the extra function call didn't matter anymore, so every test (except 3) ran faster.

PHP 5.3.2-1ubuntu4.2 on a Pentium M 1.6GHz
Elapsed (1): 0.97393798828125 / 0.9062979221344
Elapsed (2): 0.39448714256287 / 0.86932587623596
Elapsed (3): 0.44513893127441 / 0.23662400245667
Elapsed (4): 0.38685202598572 / 0.82854390144348
Speculation: Casting an array is slower, casting an object can be faster, but might not be slower.

PHP 5.2.6-1+lenny8 on a Xeon 5110
Elapsed (1): 0.273758888245 / 0.530702114105
Elapsed (2): 0.276469945908 / 0.605964899063
Elapsed (3): 0.332523107529 / 0.137730836868
Elapsed (4): 0.267735004425 / 0.556323766708
Speculation: These results are similar to Artefacto's results, I think it's PHP 5.2.

解决方案: 我使用的分析器(Xdebug)使函数调用慢了约3倍(即使没有分析),但是没有明显影响转换和比较,所以转换和比较看起来更快,即使它不是受调试器/分析器影响.

Answer 1

我实在无法重现。事实上，除了一种情况外，你的策略给了我更长的时间：

<?php

class A {
    private $a = 4;
    private $b = 4;
    private $f = 7;
}

$arr = array("a" => 4, "b" => 4, "f" => 7);

$obj = new A();

$t = microtime(true);

for ($i = 0; $i < 500000; $i++) {
    is_array($obj) and die("err");
}

echo "Elapsed (1.1): " . (microtime(true) - $t);
echo "\n";

$t = microtime(true);

for ($i = 0; $i < 500000; $i++) {
    ($obj === (array) $obj) and die("err");
}

echo "Elapsed (1.2): " . (microtime(true) - $t);
echo "\n";

$t = microtime(true);

for ($i = 0; $i < 500000; $i++) {
    is_object($arr) and die("err");
}

echo "Elapsed (2.1): " . (microtime(true) - $t);
echo "\n";

$t = microtime(true);

for ($i = 0; $i < 500000; $i++) {
    ($arr === (object) $arr) and die("err");
}

echo "Elapsed (2.2): " . (microtime(true) - $t);
echo "\n";

$t = microtime(true);

for ($i = 0; $i < 500000; $i++) {
    is_object($obj) or die("err");
}

echo "Elapsed (3.1): " . (microtime(true) - $t);
echo "\n";

$t = microtime(true);

for ($i = 0; $i < 500000; $i++) {
    ($obj === (object) $obj) or die("err");
}

echo "Elapsed (3.2): " . (microtime(true) - $t);
echo "\n";

$t = microtime(true);

for ($i = 0; $i < 500000; $i++) {
    is_array($arr) or die("err");
}

echo "Elapsed (4.1): " . (microtime(true) - $t);
echo "\n";

$t = microtime(true);

for ($i = 0; $i < 500000; $i++) {
    ($arr === (array) $arr) or die("err");
}

echo "Elapsed (4.2): " . (microtime(true) - $t);

输出：

经过（1.1）：0.366055965424
经过（1.2）：0.550662994385
经过（2.1）：0.337422132492
经过（2.2）：0.579686880112
经过（3.1）：0.402997970581
经过（3.2）：0.190818071365
经过（4.1）：0.332742214203
经过（4.2）：0.549873113632

强制转换和比较只是为了检查某物是否是对象而更快。猜测如下：也许是因为对象身份检查只需要确定处理程序表和对象句柄是否相同，而检查数组身份在最坏的情况下需要比较所有值。