是foreach(在这种情况下为PHP5)的数组的“副本”是具有实际开销的直接副本,还是仅是懒惰的副本(写时复制),它仅在检测到写操作时才产生开销？
另一种方法,在多个地方都应注意,是在key($array)上运行foreach －那怎么会更快呢？
解决方法:
好吧,所以我去测量了一下
Test This And This And, uh, This
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Setup Setup Setup
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$i = array_fill(0,1000,'1'); $j = array_fill(0,1000,'1'); $j = array_fill(0,1000,'1');
$c = 0; $d = 0; $e = 0;
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Code Under Test Code Under Test Code Under Test
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foreach ($i as $v) foreach (array_keys($j) as $k) foreach ($i as &$v)
{ $c+= $v; } { $d+= $j[$k]; } { $e+= $v; }
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Tear Down Tear Down Tear Down
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print "c = $c"; print "d = $d"; print "e = $e";
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Test for repetitions. 10000
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c = 10000000 d = 10000000 e = 10000000
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Ran in 1.8540189266205 Ran in 4.0039160251617 Ran in 1.9633851051331
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Winner -0.10936617851257 Looser 2.0405309200287 2nd Best 0
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看起来foreach($a as $v)比array_keys更好,而使用& v则在中间.
