Re: Declaring and checking content of variables with consecutive names

[AnomalousMonk]

... find out (in a loop) which of those are empty?

One way for an array:

c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dump qw(dd);
 ;;
 use constant INITIALIZER => '';
 ;;
 my @strings = (INITIALIZER) x 6;
 dd \@strings;
 ;;
 @strings[1, 4] = qw(foo bar);
 dd \@strings;
 ;;
 my @empties = grep { $strings[$_] eq INITIALIZER } 0 .. $#strings;
 print qq{indices of empty elements: @empties};
"
["", "", "", "", "", ""]

["", "foo", "", "", "bar", ""]

indices of empty elements: 0 2 3 5

And a way for hashes:

c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dump qw(dd);
 ;;
 use constant INITIALIZER => '';
 ;;
 my %strings = map { $_ => INITIALIZER } 0 .. 5;
 dd \%strings;
 ;;
 @strings{1, 4} = qw(foo bar);
 dd \%strings;
 ;;
 my @empties = grep { $strings{$_} eq INITIALIZER } keys %strings;
 print qq{keys of empty values: @empties};
"
{ "0" => "", "1" => "", "2" => "", "3" => "", "4" => "", "5" => "" }

{ "0" => "", "1" => "foo", "2" => "", "3" => "", "4" => "bar", "5" => 
+"" }

keys of empty values: 3 0 2 5

(Keys of empty values are returned in random-ish order because hashes have no inherent ordering other than the key-value pairing of each hash element.)

Update: From Perl version 5.12 onward, keys called in list context also acts with arrays to return a list of all the indices (the "keys", get it?) of the array, so in the array example, the statement
    my @empties = grep { $strings[$_] eq INITIALIZER } keys @strings;
would have worked as well.