Re: Issues with the current varargs implementation (Was: Re: inadequate documentation for select and table.unpack)

[Nagaev Boris <bnagaev@...>]

On Tue, Jun 21, 2016 at 11:17 PM, Soni L. <fakedme@gmail.com> wrote:
>
>
> On 21/06/16 05:15 PM, Patrick Donnelly wrote:
>>
>> On Tue, Jun 21, 2016 at 3:59 PM, Sean Conner <sean@conman.org> wrote:
>>>
>>> It was thus said that the Great Patrick Donnelly once stated:
>>>>
>>>> On Tue, Jun 21, 2016 at 3:22 PM, Soni L. <fakedme@gmail.com> wrote:
>>>>>
>>>>> But varargs (and thus varargs-based arrays) are nil-safe by default.
>>>>
>>>> Show me in the manual where it says **tables** are not nil safe and
>>>> I'll stop posting to lua-l*.
>>>
>>>    Lua 5.3, section 3.4.7:
>>>
>>>          Unless a __len metamethod is given, the length of a table t is
>>> only
>>>          defined if the table is a sequence, that is, the set of its
>>> positive
>>>          numeric keys is equal to {1..n} for some non-negative integer n.
>>> In
>>>          that case, n is its length. Note that a table like
>>>
>>>               {10, 20, nil, 40}
>>>
>>>          is not a sequence, because it has the key 4 but does not have
>>> the
>>>          key 3.  (So, there is no n such that the set {1..n} is equal to
>>> the
>>>          set of positive numeric keys of that table.) Note, however, that
>>>          non-numeric keys do not interfere with whether a table is a
>>>          sequence.
>>>
>>>    But for this discussion:
>>>
>>> function foo(...) print(select('#',...) end
>>> function bar(t)   print(#t)             end
>>>
>>> foo(1,2,3,4)
>>> 4
>>> bar{1,2,3,4}
>>> 4
>>> foo(nil,nil,3,nil)
>>> 4
>>> bar{nil,nil,3,nil}
>>> 0
>>
>> There's an echo in this room. Apparently emphasizing **tables** is
>> lost on people so let me be crystal clear: table length is only
>> defined for sequences. __So__, while sequences are not nil-safe, that
>> does __not__ mean tables are not nil-safe.
>>
> Thus, tables are not suitable as proper arrays.

Why do you want to put nil into a proper array? For me, a proper array
is an array of elements of same type, e.g. array of integers. If some
element in an array is nil (and other are not nil), there is no single
type for all elements, so it is not a proper array.

>
>
> --
> Disclaimer: these emails may be made public at any given time, with or
> without reason. If you don't agree with this, DO NOT REPLY.
>
>



-- 


Best regards,
Boris Nagaev