Re: to-be-closed variables as resources from a library.

[Lars Müller <appgurulars@...>]

Usually you'd use both __close and __gc (and document prominently that
your library needs to be closed to have the resource released). Even if
the user forgets to mark their variable as to-be-closed, garbage
collection will take care of it eventually. This is also how Lua's file
handles work.

On 28.09.22 05:54, Jorge Visca wrote:
> I'm trying to understand to-be-closed variables and got a bit stumped.
>
> Let's suppose I am writing a library that produces an object that
> locks some resource I want released when the object can not be used
> anymore.
>
> ---------------------------------------------------------------------------------
>
>
> -- library
> local M = {
>     get_object = function ()
>         local obj = setmetatable( {resource=acquire_resource() },
>                 {__close=function (self)
> release_resource(self.resource) end }  )
>         return obj
>     end
> }
>
> -- user
> do
>     local obj <close> = M.get_object()
>     -- do stuff with obj
> end
> -- obj does not exist anymore and was closed
>
> ---------------------------------------------------------------------------------
>
>
> My intention was to spare the library's user from having to release
> resources, just get a variable and use it. But now if the user forgets
> to tag the variable as <close> when using my library then my __closes
> are useless!
>
> Is there a way for releasing library resources transparently for the
> user (that works better than __gc)?
>
> (I SO wanted using the <close> inside the library's method to work, it
> just made sense to me. OR just skip the <close> altogether, and if
> there's a __toclose use it when getting unreferenced).
>
>
> Jorge