为什么不能使用Perl变量的值来访问词法变量名? [英] Why can't I use a Perl variable's value to access a lexical variable name?

问题描述

为什么要打印42:

$answer = 42;
$variable = "answer";

print ${$variable} . "\n";

但这不是:

my $answer = 42;
my $variable = "answer";

print ${$variable} . "\n";

推荐答案

仅包变量(在第一个示例中声明的种类)可以通过符号引用作为目标.不能使用词法(my)变量，这就是第二个示例失败的原因.

Only package variables (the kind declared in your first example) can be targeted via symbolic references. Lexical (my) variables, cannot be, which is why your second example fails.

有关Perl中两个独立的变量系统的方式，请参见出色的文章应付范围操作.并请参见出色的为什么使用变量变量名是愚蠢的，为什么这很愚蠢. :)

See the excellent article Coping with Scoping for how the two separate variable systems in Perl operate. And see the also excellent Why it's stupid to use a variable variable name for why that's stupid. :)

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