Re: A thought about <const>

[Dibyendu Majumdar <mobile@...>]

On Mon, 10 Jun 2019 at 21:21, Coda Highland <chighland@gmail.com> wrote:
>> I am not sure of the usefulness of the proposed <const> qualifier, but
>> it got me thinking whether it might be possible to implement compile
>> time named constants using similar annotations. That is to say the
>> code would be equivalent to writing directly using literals.
>
>
> I certainly agree that compile-time named constants would be a nice thing to have, but I'm not 100% sure if it would have a measurable impact, because upvalues are also resolved at compile-time and you still have to push the value on the stack anyway. There's also not really a good way for modules to export compile-time named constants, which puts a significant limitation on how useful they are.
>

True.

> However, non-assignable variables are pretty useful. There are some compiler optimizations that can happen when you know a variable is read-only, and of course asserting that something is read-only can help avoid programming mistakes.
>
> There's also no real reason the same qualifier couldn't be used for both. It would just be part of the optimization: if a compiler can statically determine the value of an expression, it can replace it with the result of that expression, and being read-only and initialized with a literal is a good way to ensure that the value can be statically determined.
>

Which leads me to a second thought about the syntax.
If you wanted to declare a bunch of constants in one go, it might be
nicer to be able to do it with a single annotation, rather than per
variable annotation.