Re: string.byte with empty string

[Mark Meijer <meijer78@...>]

Ah yes, I didn't think of that.

2009/1/25 Kristofer Karlsson <kristofer.karlsson@gmail.com>:
> Your example returns nil, as you expect, but not for the reason you had.
> Lua and C-functions can both return 0 values.
>
> The reason your example returns nil, is because of this line:
> function type(aValue)
>
> If you instead change it to:
>
> do
>  local _type = type;
>  function type(...)
>    return _type(...);
>  end
> end
>
> print(type(string.byte("")));
>
> you will get the same behaviour as the C version, even though the new one is
> written in Lua.
>
>
> On Sun, Jan 25, 2009 at 3:38 AM, Mark Meijer <meijer78@gmail.com> wrote:
>>
>> 2009/1/24 Peter Cawley <lua@corsix.org>:
>> > On Sat, Jan 24, 2009 at 9:08 PM, Alexander Gladysh <agladysh@gmail.com>
>> > wrote:
>> >> In Lua "to return zero values" is the same as to return nil.
>> > No, they are not the same. The number of return values from a function
>> > call is corrected to number of results which the caller is expecting
>> > either by appending nils, or truncating the last value(s). In many
>> > contexts, like assigning the results of a function to variables, or
>> > performing a table index on the result of a function, the number of
>> > results is set explicitly by the caller. In other contexts, like the
>> > end of an argument list for function calls and table constructions, no
>> > appending or truncating is done.
>> >
>> > Hence the visible behaviour of returning zero values is the same
>> > visible behaviour as returning nil, in certain contexts. In all
>> > contexts, the non-visible behaviour is different, and in some
>> > contexts, the visible behaviour is different.
>>
>> I think that general observation is mostly a result of the difference
>> between how C functions work with Lua and how Lua functions work. For
>> example consider the following:
>>
>> do
>>  local _type = type;
>>  function type(aValue)
>>    return _type(aValue);
>>  end
>> end
>>
>> print(type(string.byte("")));
>>
>> I'm not in a position to test it but it should print nil, instead of
>> an error, due to that seemingly pointless Lua wrapper around the C
>> function type().
>
>