Re: [ANN] Lua 5.4.0 (work1) now available

[Russell Haley <russ.haley@...>]

On Tue, Mar 13, 2018 at 6:45 PM, Coda Highland <chighland@gmail.com> wrote:

On Tue, Mar 13, 2018 at 7:47 PM, Tomás Guisasola
<tomas@tecgraf.puc-rio.br> wrote:
> Hi Roberto
>
>> No, this is not like _javascript_! 'undef' is NOT a value.
>
> But it is used as a value.  It sounds strange to me...
>
>>
>> t[i]=undef is a special syntax form that means "remove the key 'i'
>> from table 't'".
>
> But it seems like an assignment.  Wouldn't be better to create a special
> syntax for removing a key from a table instead pretending it as an
> assingment?
>
> You should have considered a pair of functions, such as table.undefine(t, i)
> to undefine a key, and table.defined(t, i) to check whether the table has
> the key.  Why did you choose the assignment?
>
> Regards,
> Tomás

Functions are a bad idea, because this really is a language primitive.

Can I ask why this would be considered a primitive and not just a behaviour of tables?

If it were a function it could be re-assigned and used as a check for any bounds value or "tomb stone". It would potentially also be valid in both normal and LUA_NILINTABLE mode.

Cheers,

Russ

That said, I would have preferred a keyword operator ("delete x")
instead of a syntactic constant-ish thing. I understand why it wasn't
done -- it simplifies the grammar because it's not a new token type,
just a special case in the existing grammar, and it's mostly
backwards-compatible if you turn the feature off.

/s/ Adam