PrependUOffsetTRelativeSlot prepends an UOffsetT onto the object at
        vtable slot `o`. If value `x` equals default `d`, then the slot will
        be set to zero and no other data will be written.

def PrependUOffsetTRelativeSlot(self, o, x, d):
        """
        PrependUOffsetTRelativeSlot prepends an UOffsetT onto the object at
        vtable slot `o`. If value `x` equals default `d`, then the slot will
        be set to zero and no other data will be written.
        """

        if x != d:
            self.PrependUOffsetTRelative(x)
            self.Slot(o)