Interesting. Your Trait::Selected class looks very much like an inside-out class. In fact, using Object::InsideOut it could be implemented, very simply, as follows:

    package Trait::Selected;
        use Object::InsideOut;
        my %is_selected :Field :Acc(is_selected);
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(Of course, looking at Class::Trait, I see that it offers a lot of functionality beyond that covered by my simple example above.)

Class::Trait->apply( $some_class, 'Trait::Selected' );

Ah, sweet synergy! This prompted me to add a runtime inheritance mechanism to Object::InsideOut:

    My::Class->add_class('Trait::Selected');
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What happens when the object goes out of scope? The trait still retains that object’s selected value and it’s tricky to remove.

If done using Object::InsideOut, this is no issue at all: The trait will be automatically cleaned up when an object is destroyed.

I just uploaded Object::InsideOut v2.08 (which contains the runtime inheritance feature) to CPAN. Thanks for the idea.