assignments to nil, as a drain (Re: allowing value evaluations as statements)

[Asko Kauppi <askok@...>]

Brought me to think of this, opinions?


==== assignment to 'nil' (drain) ====

In Lua, "_= value" is often used to drain values. Or even "_,_, some=  
f()"

This is okay, but causes two problems:
- "_" needs to be declared 'local' if used with -lstrict checking
- the value _is_ actually stored, and may cause surprises (you should  
never USE it)

Allowing 'nil' to be used on left side of assignments would 'fix'  
this, providing
a value drain without readback possibility (s.a. /dev/null).

nil,nil, some= f()

Another issue is use of 'local' with such constructs:

local nil,nil, some= f()

Should the use of 'nil' be allowed there, simply ignored. Maybe not,  
this does look fishy..

So we need to also in the future:

local some
nil,nil, some= f()

One way could be officially declaring '_' as an always-local, always- 
nil drain variable. :)
This sounds un-Lua-ish, but is actually very close to how it's  
already treated.

-asko


David Manura kirjoitti 4.1.2007 kello 0.35:

> > > On 31-Dec-06, at 9:56 PM, askok <at> dnainternet.net wrote:
> > > > _= nsfm:copyPath( testfile, newfile )
> > > >     or error "File copy failed!"
> > > >
> > > > Currently, Lua does not allow leaving the "_=" away, since that
> > > > would make these commands and commands don't have a value ('or'
> > > > gives this a value).
>
> The wiki page on this is here:
>
>   http://lua-users.org/wiki/ExpressionsAsStatements
>
> -davidm