遍历 Perl 数组的最佳方法 [英] Best way to iterate through a Perl array
问题描述
遍历 Perl 数组的最佳实现方式(在速度和内存使用方面)是什么?有没有更好的办法?(@Array
不需要保留).
Which is the best implementation(in terms of speed and memory usage) for iterating through a Perl array? Is there any better way? (@Array
need not be retained).
foreach (@Array)
{
SubRoutine($_);
}
实施 2
while($Element=shift(@Array))
{
SubRoutine($Element);
}
实施 3
while(scalar(@Array) !=0)
{
$Element=shift(@Array);
SubRoutine($Element);
}
实施 4
for my $i (0 .. $#Array)
{
SubRoutine($Array[$i]);
}
实施 5
map { SubRoutine($_) } @Array ;
推荐答案
在速度方面:#1 和 #4,但在大多数情况下不会太多.
In terms of speed: #1 and #4, but not by much in most instances.
您可以编写一个基准来确认,但我怀疑您会发现 #1 和 #4 稍微快一些,因为迭代工作是在 C 而不是 Perl 中完成的,并且不会发生不必要的数组元素复制.(
$_
被 aliased 到 #1 中的元素,但 #2 和 #3 实际上 复制 数组中的标量.)You could write a benchmark to confirm, but I suspect you'll find #1 and #4 to be slightly faster because the iteration work is done in C instead of Perl, and no needless copying of the array elements occurs. (
$_
is aliased to the element in #1, but #2 and #3 actually copy the scalars from the array.)#5 可能类似.
就内存使用而言:除了 #5 之外,它们都相同.
In terms memory usage: They're all the same except for #5.
for (@a)
是特殊情况以避免数组变平.循环遍历数组的索引.for (@a)
is special-cased to avoid flattening the array. The loop iterates over the indexes of the array.在可读性方面:#1.
在灵活性方面:#1/#4 和 #5.
In terms of flexibility: #1/#4 and #5.
#2 不支持错误的元素.#2 和 #3 具有破坏性.
#2 does not support elements that are false. #2 and #3 are destructive.
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