Re: Tuples and other constant values

[Dirk Laurie <dirk.laurie@...>]

2015-07-05 20:39 GMT+02:00 Tim Hill <drtimhill@gmail.com>:
>
>> On Jul 5, 2015, at 8:59 AM, steve donovan <steve.j.donovan@gmail.com> wrote:
>>
>> On Sun, Jul 5, 2015 at 2:39 PM, Jay Carlson <nop@nop.com> wrote:
>>> Could I call a function like table.append(c, 4)?
>>
>> I think the idea of a tuple is that it is a const unmodifiable table.
>>
>>> I had a more complicated proposal for "static" which might help. "static c = Const{1,2,3}" would do the same thing, even inside a loop.
>>
>> So it would be a _compile-time_ constant? That makes it cheap to use,
>> although restricts what values it can be initialized to
>>
>
> But in Lua constants have nearly identical overhead to locals (in fact, you can think of them conceptually as read-only locals). Look carefully at the bytecode and the only real difference is a bit indicating if the source is a local (on the stack) or a constant (in the constant table for the chunk).
>
> Apart from the original OP issue of efficient memoization, I’m not really seeing anything in this thread that cannot already be done in Lua with appropriate tables and metatables, or a few good practices (use of locals etc).

The thing is that there is a whole circle of ideas that belong
together: immutable values,
non-reassignable names, tuples and probably more. Just bringing in one
of them is not
a policy.

Maybe Ravi is a better language than Lua for bringing in a "const"
keyword, since
it is already concerned with typing.