lua-users home
lua-l archive

Re: Propsoal: a lua dialect without nil

[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index] [Thread Index] 

Consider adding a new value next to "nil": "undefined".
local t = {}
print ( t["somestring"]) --- prints "undefined"
t["somestring"] = nil
print ( t["somestring"]) --- prints "nil"
Both undefined and nil evaluates to false when used in an if statement.
For loops will not stop until it encounters an "undefined" value.
Same for the # length operator.
For pairs will show all key-value pairs where the value is not undefined. Keeping it simple and making it easier to grasp, at the same time, without being pedantic. 
On 16/02/2011, at 7:50 PM, Luiz Henrique de Figueiredo wrote:

But nil isn't really first-class, because it cannot really be stored
as value into tables.
You can definitely store nil in a table in the sense that t[1]=nil gives 
you back nil when you read t[1].

"storing" it in a table makes the key go away

This reflects our view of tables, which are containers for values.
Keys play a secondary role. When there is no value, there's no key.
This behavior is *not* due to some flaw in nil.

not show up on i/pairs
One way to think about a table is that it initially contains *all* pairs (key,nil), for all possible keys. You wouldn't want pairs to show them all :-)

AltStyle によって変換されたページ (->オリジナル) /