gistfile1.nim

type MyObj = object of RootObj

method output(self: ref MyObj) =
    echo "Output something"

type ChildObj = object of MyObj
    customvar: string

method newOutput(self: ref ChildObj) =
    self.customvar = "Child output custom var too"
    
method output(self: ref ChildObj) =
    echo "Child Output something too"
    self.newOutput()
    echo self.customvar

var o = new(MyObj)
var ochild = new(ChildObj)

var objs : seq[ref MyObj] = @[]

objs.add(o)
objs.add(ochild)

for o in objs:
    o.output()