It may have a confusing behavior, not interpretation. += may mean “evaluate lvalue, add a value to it as usual and set it back”. If you end up getting confused

It may have a confusing behavior, not interpretation. += may mean “evaluate lvalue, add a value to it as usual and set it back”. If you end up getting confused by: t.x = t.x + v Then it is a question to t’s metatable designer either way.