gistfile1.txt

use v6;

multi trait_mod:<is>(Attribute:D $attr, :$providing-private-accessor! ) is export {
    my $class = $attr.package;
    my $name = $attr.name.substr(2); #drop the initial $!
    if $name ~~ $class.^private_method_table {
        die "A private method with attribute name already exists, can't create private accessor";
    } else {
        $class.^add_private_method($name, method (Mu:D:) {
            $attr.get-value( self );
        });
    }
}

my class A {
    has $!private is providing-private-accessor = 'test';

    method test(A:D: A $b) {
        say "Private value from the other class : "~$b!private;
    }
}

my $a = A.new();
my $b = A.new( private => 12 );

$a.test( $b );