That's nice for a short parameter list, but it could get bluky for large lists (like the HTML::Template constructor). I prefer something like this:

{
    my @PARAMS = qw( foo bar baz );
    sub new 
    {
        my $class = shift;
        my $in    = shift;
        my $self = { map { $_ => $in->{$_} || '' } @PARAMS };
        bless $self, $class;
    }
}
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The above is more self-documenting, because all the parameters taken are listed above the subroutine and can be easily broken into multiple lines. It also doesn't mix the parameter definitions with other code.