Re: Different shades of false

[Romulo Bahiense <romulo@...>]

Dolan, Ryanne Thomas (UMR-Student) wrote:
> Exactly.  The only problem with nil/false is that people use these values incorrectly.  nil is by no means synonomous with false, so it makes sense that nil ~= false.  Being false and not defined are two very different states.

I agree. To me, this discussion is just like the one with NULL's in 
RDBMS (1). NULL is not a value, it represents unknow, undetermined, not 
present etc. It is not 0, it is not "", it is not false (in systems that 
support boolean natively), it is not 0.0 nor it is ASCII NULL.

And to get worse, a table couldn't be checked for emptiness because it 
may have a metatable which, incidentally, may have __index and 
__newindex defined. It may be "physically" empty, but who knows what 
those methods will return?

Consider:

userOptions = {}

groupOptions = {
    sendEmail = true;
}

setmetatable(userOptions,{__index=groupOptions})

if userOptions.sendEmail then
  mail.send{to = ..., subject = ..., ...}
end


Note that userOptions has no value inside it (no key, no value) but it 
is not empty. It's "parent" metatable has the values. Also note that 
'nil' is different from 'false', because 'false' would mean the user 
don't want to receive e-mails, while 'nil' means he/she just don't care.


This discussion remembers me of some posts from The Daily WTF, where 
now-and-then some smart guy declares something like:

enum Bool = (TRUE,FALSE,MAYBE)

--rb

1. Except, of course, to the fact that in Lua, nil==nil, while in some 
RDBMS, NULL <> NULL.