Be aware that your get_ids is using map in void context.

As for the anonymous hash, you can use map in its rightful list context to create a hash without manually inserting the values.

#!/usr/bin/perl -w
use strict;

sub get_ids {
    my $hashref = shift;
    print map {"$_\n"} keys %$hashref;
    # or, depending on your tastes
    # print "$_\n" for keys %$hashref;
}

get_ids( {map {$_,1} qw(one two three)} );
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update Added link to Perl FAQ 6.

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