if ($something) {
   ...
}

##</code><code>##

has something => (
   is  => 'ro',
   isa => 'Bool',
);

##</code><code>##

has something => (
   is  => 'ro',
   isa => 'Any', # Bool
);

##</code><code>##

has something => (
   is     => 'ro',
   isa    => Bool->plus_coercions(Any, q{ !!$_ }),
   coerce => 1,
);