Wishlist proposal, documenting fn arg as in or out or mod

[Cecil Ward]

On Tuesday, 20 June 2023 at 16:18:16 UTC, Dom DiSc wrote:
> Just to put it in clearer words:
>
> On Tuesday, 20 June 2023 at 15:01:17 UTC, Cecil Ward wrote:
>> I would love to be able to document my arguments as in or out 
>> but also as read-write
>
> This is what "ref" is for.
>
>> We already have "in". Good thing.
>>
>> However it has got mixed up with const so that you can’t 
>> declare something as both.
>
> Hurray!
> I'm so glad this is not allowed. "in" means const. There is no 
> gain in "const const".
>
>> However I hate using ref for input-output arguments as it 
>> isn’t visible at the call site
>
> This is true for all annotations.
>
>> and a ref could be just ref-for-implementation
>
> Sorry, but if a function takes a "ref" that it never modifies, 
> I would call this simply a bug. It prevents you from calling it 
> with const or immutable arguments while this would be perfectly 
> valid.
> So "ref" is documenting that the function will modify this 
> parameter. You can never expect anything else (or maybe curse 
> the stupid developer that missed marking the parameter as 
> const).

We seem to have very different approaches. I like the fact that 
const prevents me from modifying the argument inside the 
function. I use that a lot. I never use ref apart from 
by-ref-performance cases, although really the compiler should 
deal with that and split the passing strategies according to the 
size of the object in question.

You’re wrong about the call site because I always then use 
pointers and an & is visible at the call site. And there’s not so 
much danger in a const pointer argument as there cannot be any 
pointer modification although it can be stored externally which 
is potentially bad.

I’m not a C++ programmer and the first time I ever looked at it I 
looked at &-ref and screamed, it’s like var parameters in Pascal 
etc. C is just about all I known.

So you can see I’m a dinosaur and am keeping it C-like by 
default, unless I can see a good reason not to. Even though there 
are so many things I am not too happy with in C now that I’ve 
seen D and am starting to feel my way around it.