enum OTHER, OPERATION

function operation(object o)
    integer rid = o[OPERATION]
    if rid!=NULL then
        return call_func(rid,{})
    end if
    return "no implementation"
end function

function xthing()
    return "default implementation"
end function

function newX()
    return {1,routine_id("xthing"),2}
end function

function newY()
    object res = newX()
    res[OTHER] = "something else"
    -- remove delegate:
    res[OPERATION] = NULL
    return res
end function

function zthing()
    return "delegate implementation"
end function

function newZ()
    object res = newX()
    -- replace delegate:
    res[OPERATION] = routine_id("zthing")
    return res
end function

object x = newX(),
       y = newY(),
       z = newZ()

?operation(x)
?operation(y)
?operation(z)