# Pastebin gejB2EdA
$ perl6 -Ilib -MRed -e '
model B { has $.a is column }

model A {
   has $.a is column;
   has B::ResultSet $.b = .where: .of.a == $!a;
}

say A.new: :1a;


'
Type check failed in assignment to $!b; expected B::ResultSet but got B::ResultSet.new(filter => Red::F...
  in block <unit> at -e line 9