Possible 'pure' bug with int[] slice. Programming in D page 174

[Alex Bryan]

On Saturday, 4 October 2025 at 12:40:43 UTC, Brother Bill wrote:
> On Saturday, 4 October 2025 at 12:14:06 UTC, Dmitry Olshansky 
> wrote:
>> It’s weakly pure in that it could only mutate things that are 
>> passed in. Strongly pure would require no mutable 
>> pointers/slices/references.
>> It may be misleading that it’s single keyword for both of 
>> these. The good news is that strongly pure functions can call 
>> weakly pure function and stay strongly pure.
>
> So if we don't want to allow mutating passing in parameters, 
> add 'in' keyword to each parameter.  Then it should be strongly 
> cure.  Is that correct?
> ```
> int[] inner(in int[] slice) pure
> ```

If you want to enforce (and also document) that an parameter is 
never changed by the function, you should use `const`. If I'm 
reading the spec correctly 
(https://dlang.org/spec/function.html#in-params), `in` always 
implies `const`, and with the -preview=in compiler switch, it 
also implies `scope`