Re: Yet another proposal for <toclose> (was Re: [ANN] Lua 5.4.0 (alpha) now available)

[pocomane <pocomane_7a@...>]

On Sat, Jun 29, 2019 at 1:12 AM Sergey Kovalev <kovserg33@gmail.com> wrote:
>
> > The proposed 'defer' statement looks like this:
> >
> > defer ... end
> >
> > with the guarantee that f will be invoked at scope exit.
> >

I think that <toclose> is more powerful since it let you to define an
object in a scope, but close it in another one. E.g. (I already wrote
something like this in another post):

local function my_complex_object()
  local result = {} -- NOT <toclose>
  -- ...
  return setmetatable( result, {__close = my_finalizer } )
end

do
  local <toclose> obj = my_complex_object()
  -- ... use obj as you wish, it will be close at end of THIS scope
end

Of course you can simulate this with defer

local obj = my_complex_object()
defer getmetatable(obj).__close() end

but the api/protocol is up to you, while with <toclose> there is a
single mechanism that will be shared among all the lua libraries.
(I.e. with defer, someone would use a finalize method, others a
metamethod, others an additional return value, and so on).

However, I found a Go-like defer more elegant too (and probably more
"luaish"). So probably this is a issue of tradeoff... for now I am
slightly more incline to <toclose>.