{
        my %SELF = map { $_ => '' } qw( foo bar baz );
        sub new {
            my $self = bless { %SELF } => shift;
            @$self{keys %SELF) = @{+shift}{keys %SELF};
            return $self;
        }
    }

##</code><code>##

    {
        my %SELF = (
                foo => 0,
                bar => "",
                baz => [],
        );
        sub new {
            my $self = bless {} => shift;
            my %p = @_;

            croak("...") if keys %p > keys %SELF;
            # If given a bad key.

            $self->$_($p{$_}) foreach keys %p; # Lazy. Damn lazy.

            return $self;
        }
    }

##</code><code>##

    sub new {
        my $self = bless {
            foo => 0,
            bar => "",
            baz => [],
            this_should_not_be_touched_here => {},
        } => shift;
        my %p = @_;

        $self->{$_} = delete $p{$_}
            for grep exists $p{$_} => qw/ foo bar baz /;
            # Note, this list doesn't equal keys(%$self).

        croak("Unknown parameters: @{[keys %p]}")
            if %p;

        return $self;
    }