example of a simple "is tracked" trait in development

gistfile1.txt

class Foo {

    has $.a;
    has $.b;
    has $.c;
    has $.changed = False;

    method a { self!proxy($!a) }
    method b { self!proxy($!b) }
    method c { self!proxy($!c) }

    method !proxy(\attr) {
        Proxy.new(
           FETCH => -> { attr },
           STORE => -> $, $value { $!changed = True; attr = $value }
        );
    }
}

my $f = Foo.new( a => 42, b => 666 );
say $f.changed;

$f.a = 67;
say $f.changed;

$f.perl.say;