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

[Sean Conner <sean@...>]

It was thus said that the Great Coda Highland once stated:
> On Tue, Oct 6, 2015 at 10:15 AM, Sean Conner <sean@conman.org> wrote:
> > 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
> >
> 
> Solution: Don't call it __serialize! Call it __json, __bson, __cbor,
> or whatever's actually appropriate for the format.
> 
> You could borrow a Pythonism and use __repr for Lua syntax.

  I actually like this idea, but it's unclear whether we can use those
names.  I checked the Lua manual (5.3) and the only thing Lua reserves are
the keywords 

     and       break     do        else      elseif    end
     false     for       function  goto      if        in
     local     nil       not       or        repeat    return
     then      true      until     while

and any itentifier with the following pattern:

	'_' [A-Z]*

  There's no mention of Lua reserving any identifiers with '__' (two
underscores).

  -spc