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    GetOptions(
        'f'     => \my $filename,
...
        maybe baz      => $batman,
        maybe universe => $universe,
    )

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

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

sub foo( %options ) {
    ...
}

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

sub foo( %options ) {
    option baz      => 'Superman',
...

    return \%options
}

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

use 5.020;
use feature 'signatures';
...
#is $f->foo( baz => undef ), { baz => undef, universe => 'meth_DC' }, 
+'Positional parameters work';

done_testing;