GetOptions(
        'f'     => \my $filename,
        'bar'   => \my $bar,
        'bruce' => \my $batman,
        'u'     => \my $universe,
    );

    foo(
              file     => $filename,
        maybe bar      => $bar,
        maybe baz      => $batman,
        maybe universe => $universe,
    )

##</code><code>##

sub foo( %options ) {
    if( ! exists $options{ baz } ) {
        $options{ baz } = 'Superman';
    };
    ...
}

##</code><code>##

sub foo( :$baz = 'Superman', :$bar, :$file, :$universe='DC' ) {
}

##</code><code>##

sub foo( %options ) {
    ...
}

##</code><code>##

sub option ( $key, $def, $options ) {
    if( !exists $options->{ $key } ) {
        $options->{ $key } = $def;
    }
    return $options
}

##</code><code>##

sub foo( %options ) {
    option baz      => 'Superman',
    option universe => 'DC',
           \%options;

    return \%options
}

##</code><code>##

    option files => [glob('~/*')],
    option html  => $user_agent->get('https://example.com'),

##</code><code>##

use 5.020;
use feature 'signatures';
no warnings 'experimental::signatures';
use Carp 'croak';

sub option ( $key, $def, $options ) {
    if( !exists $options->{ $key } ) {
        $options->{ $key } = $def;
    }
    return $options
}

sub required ( $key, $options ) {
    if( !exists $options->{ $key } ) {
        croak sprintf 'Need the "%s" option passed in', $key;
    }
    return $options
}

sub foo( %options ) {
    option baz      => 'Superman',
    option universe => 'DC',
           \%options;

    return \%options
}

sub req( %options ) {
    required 'run',
    option baz      => 'Superman',
           \%options;

    return \%options
}

use Test2::V0 '-no_srand';

is option('baz' => 'default', {}), { baz => 'default' }, 'Setting a default';
is foo(), { baz => 'Superman', universe => 'DC' }, 'Default values';
is foo(baz => 0), { baz => '0', universe => 'DC' }, 'False value';
is foo(baz => undef), { baz => undef, universe => 'DC' }, 'Undef but present value is kept';
is foo(baz => undef), { baz => undef, universe => 'DC' }, 'Undef but present value is kept';

ok dies { req( baz => 'Wonderwoman' ) }, 'A missing obligatory option dies';
ok lives { req( run => undef, baz => 'Wonderwoman' ) }, 'Passing the obligatory option lives, even if undefined';

#class cfoo 0.01 {
#    field $baz;
#    field $universe;
#
#    method foo( $self, %options ) {
#        option baz      => $self->baz,
#        option universe => $self->universe,
#        \%options;
#
#        return \%options
#    }
#}
#my $f = cfoo->new( baz => 'objSuperman', universe => 'DC' );
#is $f->foo( baz => undef ), { baz => undef, universe => 'meth_DC' }, 'Positional parameters work';

done_testing;