From zefram@fysh.org

$ ./perl6 -e 'sub aa(int​:U $i) { say $i; }; aa(3); aa(int)'
3
Cannot unbox a type object
  in sub aa at -e​:1
  in block <unit> at -e​:1

The definedness constraint qualifiers :D and :U are ignored for the int
type, even though in this context of a parameter declaration they work
for most types. This is misleading. The qualifiers should signal an
error in this situation, unless and until they are implemented so as to
have the obvious effect.

-zefram

From @jnthn

On Mon Sep 21 11​:22​:24 2015, zefram@​fysh.org wrote​:

$ ./perl6 -e 'sub aa(int​:U $i) { say $i; }; aa(3); aa(int)'
3
Cannot unbox a type object
in sub aa at -e​:1
in block <unit> at -e​:1

The definedness constraint qualifiers :D and :U are ignored for the int
type, even though in this context of a parameter declaration they work
for most types. This is misleading. The qualifiers should signal an
error in this situation, unless and until they are implemented so as to
have the obvious effect.

A native type cannot hold an undefined value, so writing :U should be a compile time error (it could never match, so probably indicates confusion). May as well do similar for :D.

/jnthn

The RT System itself - Status changed from 'new' to 'open'

From zefram@fysh.org

jnthn@​jnthn.net via RT wrote​:

A native type cannot hold an undefined value, so writing :U should
be a compile time error (it could never match

I would expect the type object (int) to match the notional int​:U
constraint. Rakudo is quite clear that (int) isa int, and obviously
it's not defined in the relevant sense.

$ ./perl6 -e 'say int ~~ int; say int.defined'
True
False

This side of native types runs into [perl #​126116], regarding inconsistent
behaviour about whether the type object is allowed into a native-typed
variable.

-zefram