From @zoffixznet

m​: class C { method foo (--> :​:?CLASS​:D) { self } }; say .foo given C
rakudo-moar 080630​: OUTPUT«(C)␤»

Expected​: typecheck failure, since `self` is not :D

And using :​:?CLASS​:D in the body of the method errors out, saying you
can't adverb :​:?CLASS​:

m​: class C { method foo (--> :​:?CLASS​:D) { say (​::?CLASS​:D).HOW; self;
} }; say .foo given C
rakudo-moar 080630​: OUTPUT«5===SORRY!5=== Error while compiling
<tmp>␤You can't adverb :​:?CLASS␤at <tmp>​:1␤------> 3d foo (-->
:​:?CLASS​:D) { say (​::?CLASS​:D7⏏5).HOW; self; } }; say .foo given C␤
expecting any of​:␤ pair value␤»

https://irclog.perlgeek.de/perl6/2016-11-22#i_13611710