foreach、带有 lambda 的 array_map 和带有静态函数的 array_map 的性能 [英] Performance of foreach, array_map with lambda and array_map with static function
问题描述
这三种用于将数组转换为另一个数组的方法之间的性能差异(如果有的话)是什么?
What's the performance difference (if there is any) between these three approaches, both used to transform an array to another array?
- 使用
foreach - 将
array_map与 lambda/闭包函数一起使用 - 将
array_map与静态"函数/方法一起使用 - 还有其他方法吗?
- Using
foreach - Using
array_mapwith lambda/closure function - Using
array_mapwith 'static' function/method - Is there any other approach?
为了清楚起见，让我们看一下示例，所有示例都执行相同的操作 - 将数字数组乘以 10:
To make myself clear, let's have look at the examples, all doing the same - multiplying the array of numbers by 10:
$numbers = range(0, 1000);
<小时>
Foreach
$result = array();
foreach ($numbers as $number) {
$result[] = $number * 10;
}
return $result;
<小时>
使用 lambda 映射
return array_map(function($number) {
return $number * 10;
}, $numbers);
<小时>
使用静态"函数映射，作为字符串引用传递
function tenTimes($number) {
return $number * 10;
}
return array_map('tenTimes', $numbers);
<小时>
还有其他方法吗?我会很高兴听到上述案例之间的所有差异，以及为什么应该使用一个而不是其他的任何输入.
Is there any other approach? I will be happy to hear actually all differences between the cases from above, and any inputs why one should be used instead of others.
推荐答案
FWIW，我只是做了基准测试，因为海报没有做.在 PHP 5.3.10 + XDebug 上运行.
FWIW, I just did the benchmark since poster didn't do it. Running on PHP 5.3.10 + XDebug.
更新 2015-01-22 与下面 mcfedr 的回答进行比较，以获得没有 XDebug 和更新的 PHP 版本的额外结果.
UPDATE 2015-01-22 compare with mcfedr's answer below for additional results without XDebug and a more recent PHP version.
function lap($func) {
$t0 = microtime(1);
$numbers = range(0, 1000000);
$ret = $func($numbers);
$t1 = microtime(1);
return array($t1 - $t0, $ret);
}
function useForeach($numbers) {
$result = array();
foreach ($numbers as $number) {
$result[] = $number * 10;
}
return $result;
}
function useMapClosure($numbers) {
return array_map(function($number) {
return $number * 10;
}, $numbers);
}
function _tenTimes($number) {
return $number * 10;
}
function useMapNamed($numbers) {
return array_map('_tenTimes', $numbers);
}
foreach (array('Foreach', 'MapClosure', 'MapNamed') as $callback) {
list($delay,) = lap("use$callback");
echo "$callback: $delay
";
}
我通过十几次尝试得到了 100 万个数字的非常一致的结果:
I get pretty consistent results with 1M numbers across a dozen attempts:
- Foreach:0.7 秒
- 关闭地图:3.4 秒
- 映射函数名称:1.2 秒.
假设关闭时地图速度慢是由于可能每次都在评估关闭造成的，我也这样测试:
Supposing the lackluster speed of the map on closure was caused by the closure possibly being evaluated each time, I also tested like this:
function useMapClosure($numbers) {
$closure = function($number) {
return $number * 10;
};
return array_map($closure, $numbers);
}
但结果是相同的，确认闭包只计算一次.
But the results are identical, confirming that the closure is only evaluated once.
2014-02-02 更新:操作码转储
2014-02-02 UPDATE: opcodes dump
这是三个回调的操作码转储.首先useForeach():
Here are the opcode dumps for the three callbacks. First useForeach():
compiled vars: !0 = $numbers, !1 = $result, !2 = $number
line # * op fetch ext return operands
---------------------------------------------------------------------------------
10 0 > EXT_NOP
1 RECV 1
11 2 EXT_STMT
3 INIT_ARRAY ~0
4 ASSIGN !1, ~0
12 5 EXT_STMT
6 > FE_RESET $2 !0, ->15
7 > > FE_FETCH $3 $2, ->15
8 > OP_DATA
9 ASSIGN !2, $3
13 10 EXT_STMT
11 MUL ~6 !2, 10
12 ASSIGN_DIM !1
13 OP_DATA ~6, $7
14 14 > JMP ->7
15 > SWITCH_FREE $2
15 16 EXT_STMT
17 > RETURN !1
16 18* EXT_STMT
19* > RETURN null
然后是 useMapClosure()
compiled vars: !0 = $numbers
line # * op fetch ext return operands
---------------------------------------------------------------------------------
18 0 > EXT_NOP
1 RECV 1
19 2 EXT_STMT
3 EXT_FCALL_BEGIN
4 DECLARE_LAMBDA_FUNCTION '%00%7Bclosure%7D%2Ftmp%2Flap.php0x7f7fc1424173'
21 5 SEND_VAL ~0
6 SEND_VAR !0
7 DO_FCALL 2 $1 'array_map'
8 EXT_FCALL_END
9 > RETURN $1
22 10* EXT_STMT
11* > RETURN null
以及它调用的闭包:
compiled vars: !0 = $number
line # * op fetch ext return operands
---------------------------------------------------------------------------------
19 0 > EXT_NOP
1 RECV 1
20 2 EXT_STMT
3 MUL ~0 !0, 10
4 > RETURN ~0
21 5* EXT_STMT
6* > RETURN null
然后是useMapNamed()函数:
compiled vars: !0 = $numbers
line # * op fetch ext return operands
---------------------------------------------------------------------------------
28 0 > EXT_NOP
1 RECV 1
29 2 EXT_STMT
3 EXT_FCALL_BEGIN
4 SEND_VAL '_tenTimes'
5 SEND_VAR !0
6 DO_FCALL 2 $0 'array_map'
7 EXT_FCALL_END
8 > RETURN $0
30 9* EXT_STMT
10* > RETURN null
和它调用的命名函数，_tenTimes():
and the named function it calls, _tenTimes():
compiled vars: !0 = $number
line # * op fetch ext return operands
---------------------------------------------------------------------------------
24 0 > EXT_NOP
1 RECV 1
25 2 EXT_STMT
3 MUL ~0 !0, 10
4 > RETURN ~0
26 5* EXT_STMT
6* > RETURN null
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