'Allocate a new set instance pointing to an existing payload
(a meminfo pointer).
Note the parent field has to be filled by the caller.'

@classmethod
def from_meminfo(cls, context, builder, set_type, meminfo):

    self = cls(context, builder, set_type, None)
    self._set.meminfo = meminfo
    self._set.parent = context.get_constant_null(types.pyobject)
    context.nrt.incref(builder, set_type, self.value)
    return self
