return mt.Flags&1 != 0
}
func (mt *MapType) IndirectElem() bool { // store ptr to elem instead of elem itself
	return mt.Flags&2 != 0
}
func (mt *MapType) ReflexiveKey() bool { // true if k==k for all keys
	return mt.Flags&4 != 0
}
func (mt *MapType) NeedKeyUpdate() bool { // true if we need to update key on an overwrite
	return mt.Flags&8 != 0
}