Update: The common way to have a boolean yes/no attribute in Moose would be something like

    package Thing;
    use Moose;
    use Moose::Util::TypeConstraints qw{ enum };

    has delete => (is       => 'ro',
                   isa      => enum([qw[ yes no ]]),
                   init_arg => undef,
                   lazy     => 1,
                   builder  => '_build_delete');

    has _delete => (is       => 'ro',
                    isa      => 'Bool',
                    init_arg => 'delete');

    sub _build_delete {
        my ($self) = @_;
        $self->_delete ? 'yes' : 'no'
    }
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I'm a bit uncomfortable with _delete having a constructor argument delete that has the same name as an attribute that has no init argument, but it seems to work.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]