Re: Definition of table.insert

[David Kastrup <dak@...>]

Alexander Gladysh <agladysh@gmail.com> writes:

> On Sat, Jan 8, 2011 at 14:40, David Kastrup <dak@gnu.org> wrote:
>> Alexander Gladysh <agladysh@gmail.com> writes:
>
>>> On Sat, Jan 8, 2011 at 13:28, David Kastrup <dak@gnu.org> wrote:
>>>> GrayFace <sergroj@mail.ru> writes:
>>>>> On 08.01.2011 14:34, David Kastrup wrote:
>
>>>>>> I think it should be defined as a straight noop not changing the table
>>>>>> at all, ever.
>
>>>> insert(t,n,somefunction(...))
>
>>>> where somefunction may decide not to return a value.
>
>>> You can not be sure what user meant by this. Perhaps he does want to
>>> insert nil.
>
>> There is no way to insert nil in a table.  No matter what the user
>> wants.
>
> Hmm. Why not?
>
> t = { 1, 2, 3, 4, 5 }
> print("Before:", unpack(t, 1, 5))
> for i = #t, 3, -1 do
>   t[i + 1] = t[i]
> end
> t[3] = nil
> print("After:", unpack(t, 1, 6))
>
> (Strictly speaking that is not a nil, but a "hole", but that is matter
> of terminology.)

No, it isn't.  If I now do t[4]=nil; t[5]=nil; t[6]=nil I have _not_
touched t[3] at all, but clearly the table ends up with length 2.  So
there definitely has not been a value at index 3.

-- 
David Kastrup