Can I know why there is no such operators as ++ or += (or similarly others like string concatenation) in Lua?
I think the best argument for not including compound assignments in Lua is that they're an awkward companion for multi-value returns. Specifically, we need sensible rules governing how the compiler should handle the following:
I've played around with a couple different semantics -- and all of them feel like kludgy additions to an otherwise very elegant language.
But if you're willing to give up a bit of elegance, there's a couple different lua patches posted that add compound assignments to the language, including one by me. See: