Thanks! I tried the "derived" version earlier, but with stack allocated
objects, and I did not manage to get dispatch working correctly at callsite.
But after changing to ref values, it works. Is ref values required to
differentiate sub-types?
type
# If I remove ref from base, A and B
# no output is printed
Base = ref object of RootObj
A = ref object of Base
a_value: int
B = ref object of Base
b_value: int
proc test(arg: int): Base =
if arg < 0: return A(a_value: arg)
else: return B(b_value: arg)
let a = test(10)
if a of A:
echo "Got A ",A(a).a_value
if a of B:
echo "Got B ",B(a).b_value
