The hypothetical __serialize metamethod (was Re: [ANN] luaproc 1.0-4)

[Sean Conner <sean@...>]

It was thus said that the Great Andrew Starks once stated:
> On Tue, Oct 6, 2015 at 11:12 AM, Rena <hyperhacker@gmail.com> wrote:
> > I think you could use a __serialize metamethod here, when you don't have a
> > built-in handler. Then userdata, magic tables and other objects could define
> > handlers as easily as they do other metamethods.
> 
> I've often used __tostring for this, but then that wrecks my (often
> needed) method for pretty printing. I'm also guilty(?) of using two
> underscores, which I believe is, by documentation (?), reserved for
> the language. But I do it too...
> 
> Overall, however, a serialize metamethod has been my preferred way of
> figuring this stuff out. We also found ourselves wanting to know if
> the message was going inter-process or just inter-thread, but that's
> too fancy for this purpose.

  But wouldn't there have to be a consensus as to *what* __serialize
returns?  I mean, obviously, a string of byte values (variation on a string)
but the actual contents can vary widely.  Given a simple Lua table:

	{ 1 , "two" , true }

  One person might want to serialize that as JSON:

	[ 1 , "two" , true ]

  Someone else might want BSON [1] (hex dump follows):

	13 00 00 00 04 00 0D 00 
	00 00 30 00 01 00 00 00 
	31 00 74 77 6F 32 01

  Another one (like me) might want to serialize to CBOR [2] (hex dump
follows):

	83 01 63 74 77 6F F5

and yet another might want straight up Lua:

	{ 1 , "two" , true }

  Is it better to perhaps just reserve "__serialize" for serialization and
leave it up to modules to flesh it out?  Or do we need to actually define
the output format?

  -spc (Not a proposal, just something to talk about ... )

[1]	http://bsonspec.org/spec.html

[2]	RFC-7049