Re: [ANN] Lua 5.4.0 (work1) now available

[Sean Conner <sean@...>]

It was thus said that the Great albertmcchan once stated:
> On Mar 14, 2018, at 5:33 PM, Gavin Wraith <gavin@wra1th.plus.com> wrote:
> 
> > 
> > It seems to me that the proposed syntax "x = undef" looks like
> > an assignment of a value. Why not "x undef" or "undef x"? Or have
> > I missed that discussion? Sorry for the noise if I have.
> > -- 
> > Gavin Wraith (gavin@wra1th.plus.com)
> > Home page: http://www.wra1th.plus.com/
> > 
> 
> what is so bad about the old syntax x = nil ?
> 
> false were added in lua to "store" nil in table, there is no need for undef.
> 
> I am curious, is there an example where undef is truly needed ?

  Assume you have the following JSON:

	[ 1 , 2 , true , false , nil , "alpha" , "beta" ]

  Under the current (5.3) behavior, you can convert this to the following
Lua table:

	{ 1 , 2 , true , false , nil , "alpha" , "beta" }

but the length is undefined, because the nil creates a hole.  If you use
false instead:

	{ 1 , 2 , true , false , false , "alpha" , "beta" }

the length *is* defined, but it may not have the same semantic meaning. 
Now, with the proposed undef (which seems to be confusing a lot of people),
the Lua table:

	{ 1 , 2 , true , false , nil , "alpha" , "beta" }

would have a defined length and semantically matches the original JSON.

  -spc