为什么在这种情况下Perl可以自动生存? [英] Why does Perl autovivify in this case?

问题描述

为什么$a成为arrayref?我什么都没推.

Why does $a become an arrayref? I'm not pushing anything to it.

perl -MData::Dumper -e 'use strict; 1 for @$a; print Dumper $a'
$VAR1 = [];

推荐答案

这是因为for循环将@$a的内容视为左值，您可以将其赋值.请记住，for将数组的内容别名为$_.看起来即使在没有别名的内容的情况下，在@$a中查找可别名内容的行为也足以引起自动生存.

It is because the for loop treats contents of @$a as lvalues--something that you can assign to. Remember that for aliases the contents of the array to $_. It appears that the act of looking for aliasable contents in @$a, is sufficient to cause autovivification, even when there are no contents to alias.

这种混叠的效果也是一致的.以下还会导致自动生存:

This effect of aliasing is consistent, too. The following also lead to autovivification:

• map {stuff} @$a;
• grep {stuff} @$a;
• a_subroutine( @$a);

• map {stuff} @$a;
• grep {stuff} @$a;
• a_subroutine( @$a);

如果要管理自动生存，可以使用同义的编译指示来实现词法控件

If you want to manage autovivification, you can use the eponymous pragma to effect lexical controls.

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