如何在perl 5.24中关闭“何时处于实验状态……”？

Question

The code below was copied directly from the current perlsyn page on perldoc.perl.org. [I've added an initialization and declarations as needed to make it run (and it works as expected), but the point is the 'when' keyword]

Perl 5.24 complains about 'when' being experimental. Fair enough, but I don't want to see this every time I use the keyword.

no warnings qw(experimental::when) does not work - "Unknown warning category ..."

I also tried "switch" as the category

Is there another way to suppress this warning (other than disabling warnings in general)?

use v5.14;
for ($var) {
    $abc = 1 when /^abc/;
    $def = 1 when /^def/;
    $xyz = 1 when /^xyz/;
    default { $nothing = 1 }
}

Answer 1

You can enable this construct without warnings via

use experimental 'switch';

or merely disable the "experimental" warning category via

no warnings 'experimental::smartmatch';

(see the full list of available warning categories in perldoc warnings ).

But please note that smartmatch, given , and when constructs are considered to be fundamentally broken, and are being removed/redesigned. Just silencing the warning will break your code when you run that code on other perl versions.

Instead, please prefer out to spell this code out explicitly:

for ($var) {
    if    (/^abc/) { $abc = 1 }
    elsif (/^def/) { $def = 1 }
    elsif (/^xyz/) { $xyz = 1 }
    else { $nothing = 1 }
}

Yes, it's more ugly, but it will also work for all values of $var and for all Perl5 versions.

Answer 2

given和when是smartmatch实验的一部分，因此可以使用以下命令禁用这些警告：

no warnings qw( experimental::smartmatch );