Re: Why is implicit and explicit 'nil' treated differently?

[Jan Behrens <jbe-lua-l@...>]

Hi,

With "none" I meant the absence of a value. There is no value "none",
I'm sorry if I caused any confusion. However, in the C-API there is a
constant LUA_TNONE (in addition to LUA_TNIL, LUA_TBOOLEAN, etc.) to
distinguish between "no value at the given stack position" and "nil at
the given stack position".

I hope this clarifies my usage of the term "none".

Regards,
Jan


On Mon, 20 Apr 2015 15:24:45 +0200
Robert Virding <rvirding@gmail.com> wrote:

> Where does 'none' come from? I cannot find any mention of it in the
> 5.2 manual.
> 
> Robert
> 
> 
> On 19 April 2015 at 00:19, Andrew Starks <andrew.starks@trms.com>
> wrote:
> 
> >
> >
> > On Saturday, April 18, 2015, Jan Behrens <
> > jbe-lua-l@public-software-group.org> wrote:
> >
> >> [...]
> >>
> >> Generally "nil" and "none" (none = no value) are distinct when you
> >> call a function or return from a function. However, "none" gets
> >> implicitly converted to "nil" if you store it in a variable (or
> >> table) or if you put parenthesis around it (or use it in an
> >> expression where a single value is expected).
> >>
> >> [...]
> >> [...] You can use "select" to write your own functions to
> >> distinguish between "nil" and "none":
> >>
> >> function test(...)
> >>   if select("#", ...) == 0 then
> >>     return "no value given"
> >>   elseif ... == nil then
> >>     return "nil value given"
> >>   else
> >>     return "non-nil value given"
> >>   end
> >> end
> >>
> >> [...]
> >>
> >> If you store a return value in a local variable or table, then
> >> "none" always gets automatically converted to "nil". [...]