Edit: And yeah I don't think it's anything unique to Lua, it's an implementation detail of closures and lexical scope generally. It's a non-stack wrapper for closed-over variables, the end of the introduction to chapter 25 explains:
> For locals that aren’t used in closures, we’ll keep them just as they are on the stack. When a local is captured by a closure, we’ll adopt another solution that lifts them onto the heap where they can live as long as needed.
> For locals that aren’t used in closures, we’ll keep them just as they are on the stack. When a local is captured by a closure, we’ll adopt another solution that lifts them onto the heap where they can live as long as needed.
I sort of thought about mentioning something like that; that's in what I categorize as an optimization. (A good one, since the common case is that there probably isn't a closure at all in the scope, and the entire scope can thus be moved to the stack, kept out of heap, and not GC'd, reducing GC pressure.)
Edit: And yeah I don't think it's anything unique to Lua, it's an implementation detail of closures and lexical scope generally. It's a non-stack wrapper for closed-over variables, the end of the introduction to chapter 25 explains:
> For locals that aren’t used in closures, we’ll keep them just as they are on the stack. When a local is captured by a closure, we’ll adopt another solution that lifts them onto the heap where they can live as long as needed.