Singley thing

gistfile1.txt

role Singleton {
    my $instance;
    method new(|c) {
        if not $instance.defined {
            $instance = self.bless(|c);
        }
        $instance;
    }
}

multi sub trait_mod:<is>(Method:D $m, :$single!) {
    $m.wrap(method ( $self: |c) {
        my $new-self = $self;
        if not $new-self.defined {
            $new-self = $self.new;
        }
        callwith($new-self,|c);
    });
}

class Foo does Singleton {
    has $.foo is rw;
    method say-foo() is single {
        say $!foo;
    }
}

my $a = Foo.new(foo => "this one");

Foo.say-foo;
# vim: expandtab shiftwidth=4 ft=perl6