Note that `ref` stands for "reference", not "reference counting". The behavior
will not differ between the reference counting and the mark and sweep GC.
You also do not strictly require `ref` for polymorphism to work, though this is
the most common use case; any kind of pointer (`ref`, `ptr`, `var`, or
pass-by-reference for value arguments) will work.
Example:
type
animal = object of RootObj
dog = object of animal
cat = object of animal
method say(self: animal) = discard
method say(self: dog) = echo "woof!"
method say(self: cat) = echo "meow?"
proc make_noise(a: var animal) =
a.say; a.say; a.say
proc main =
var d: dog
var c: cat
d.make_noise
c.make_noise
main()
The reason why it doesn't work without pointers is that variables that aren't
references (or somesuch) cannot themselves handle polymorphic types and will be
coerced to the supertype upon assignment by hacking off any extraneous fields
at the end of the subtype and changing the type field. Otherwise, it may be
possible that method calls would try to access fields that do not exist in
memory.
