Perl List context as hash key

Question

I have a variable which I want to take the first capture and use that as the key for a hash. I found a solution but it seems suboptimal.

My $out  = $hash{[$var =~ /(^[a-z]+)/]->[0]};

It's seems like there has to be a better way then going list->array->scalar. Maybe just list->scalar. I know that I could also capture in another variable and then use that as a key, but I want to avoid that. Is there a better way to do this?

Answer 1

无需创建数组引用。

my $out = $hash{ ($var =~ m/(^[a-z]+)/)[0] }; 

Answer 2

There's no need to cram everything into a single statement

my ($key) = $var =~ /(^[a-z]+)/;
my $out   = $hash{ $key };

but something like this would be okay

my $out;
$out = $hash{$1} if $var =~ /(^[a-z]+)/;

or possibly

my $out = $var =~ /(^[a-z]+)/ && $hash{$1};

Answer 3

What´s wrong with?

$var =~ /^([a-z]+)/;
my $out = $hash{$1};

It is useful to use the output of =~ in list context for more than one match, but for a single one?

If you are expecting the regex to not match (as suggested by other people), it will be better to check first. For instance:

if( $var =~ /^([a-z]+)/ ) {
  my $out = $hash{$1};
  ...
}

If you want a one-liner, you may use:

my $out = $hash{ ($var =~ /^([a-z]+)/)[0] };

This will give a warning if the regex does not match. It was suggested first by @tinita.