Re: How to exchange the values of a specific variable (e.g: maybe a table) between Lua_States?

[孙世龙 sunshilong <sunshilong369@...>]

>From Sean Conner:

>Or try CBOR [1].  My implementation [2][3] can handle keys other than
>strings or integers, and can even handle cycles in tables.  Encoding this
>table:
>
>        local x
>        x =
>        {
>          [1] = true,
>          [false] = "nah",
>          [true] = "one",
>          [42] = "meaning of life",
>          [math.pi] = 3.000000,
>          [math.huge] = 'too large',
>          [math.maxinteger] = 'this is fine',
>          ['NaN'] = 0/0,
>          [0] = false,
>        }
>
>is no issue.  [5]
What about such tables:
Tab = {}
Tab.self = Tab;

Thank you for your patience.

Best Regards.
Sunshilong

On Mon, Apr 26, 2021 at 5:19 AM Sean Conner <sean@conman.org> wrote:
>
> It was thus said that the Great Paul Ducklin once stated:
> > >How to exchange the values of a specific
> > variable (e.g: maybe a table) between Lua_States?
> >
> > Try dkjson.
> >
> > Encode table in state A  -> Pass JSON as a string message to state B ->
> > Decode table in state B.
> >
> > Easy.
> >
> > Obviously you can’t pass userdata keys or values in the table you send
> > across (userdata variables are typically full of pointers, malloc()ed
> > buffers and system handles, etc. ). You can only copy over only strings
> > and numbers.
>
>   Or try CBOR [1].  My implementation [2][3] can handle keys other than
> strings or integers, and can even handle cycles in tables.  Encoding this
> table:
>
>         local x
>         x =
>         {
>           [1] = true,
>           [false] = "nah",
>           [true] = "one",
>           [42] = "meaning of life",
>           [math.pi] = 3.000000,
>           [math.huge] = 'too large',
>           [math.maxinteger] = 'this is fine',
>           ['NaN'] = 0/0,
>           [0] = false,
>         }
>
> is no issue.  [5]
>
> > If you want to pass open LuaSockets, however, there is a neat trick where
> > you extract the fd from the socket in state A using the socket:getfd()
> > method, pass it as a number (it is just a numeric file handle), graft it
> > into an unconnected socket in state B using socket:setfd(), and then
> > invalidate the fd in the original socket in state A so the fd doesn’t get
> > close()d when the “donor” socket gets garbage-collected.
>
>   That works as long as the the two Lua states are in the same process.
>
>   Back in 2017 I did some playing around with serializing Lua functions [4].
> I didn't finalize anything, but I did come up with some interesting
> solutions to some of the issues.  CBOR also allows values to be semantically
> tagged.  Using this, I would encode known Lua values, like io.stdin, as a
> string, but tagged as a "Lua global".  Such semantic tagging could also be
> used for other userdata, functions, etc.
>
>   -spc
>
> [1]     Concise Binary Object Representation
>
> [2]     https://github.com/spc476/CBOR
>
> [3]     Also available via Luarocks as "org.conman.cbor".
>
> [4]     https://github.com/spc476/LuaFunctionSerialize
>
> [5]     Try that with JSON!