Re: questions about closure construction

[steve donovan <steve.j.donovan@...>]

On Tue, Mar 19, 2013 at 4:27 AM, Ross Bencina
<rossb-lists@audiomulch.com> wrote:
> function __y_bar(self) print "y" end
> function Y()
>   return { foo = __y_bar }
> end
> function Z()
>   local function __z_bar(self) print "z" end
>   return { foo = __z_bar }
> end
>
> Z runs slower than X or Y, suggesting that there is some runtime overhead in
> creating a named local variable (which surprises me, seems like a simple
> optimisation).

Yes, indeed; in Z you create a closure each time, which is a dynamic
object (much as how {} is a 'table constructor' not a 'table
literal').

I believe Lua 5.2 has made some progress in re-using closures that
have no upvalues.  LuaJIT may well optimize it to nothing ;)

steve d.