Calling assumeSorted on const(std.container.Array)

[Steven Schveighoffer]

On 3/25/23 9:45 AM, Olivier Prat wrote:

> Would someone explain the exact nature of this error as I fail to 
> understand as how just telling that an Array ConstRange is assumed to be 
> sorted actually modifies anything??

It's because a Range keeps a copy of the array (Array is a reference 
counted type). Since that is labeled `const`, then editing the Range is 
forbidden.

Inside SortedRange, it has this, which is causing the issue:

```d
     static if (isForwardRange!Range)
     @property auto save()
     {
         // Avoid the constructor
         typeof(this) result = this;
         result._input = _input.save;
         return result;
     }
```

Overwriting the input isn't possible here, because it contains a const 
member.

Now, this possibly could be fixed with something like:

`return typeof(this)(_input.save);`

But it might just push the error to another place.

The whole thing is kind of ugly.

There is a note inside the Array Range which says it's trying to work 
around some old bug that is now marked as "works for me", so maybe that 
can be reexamined.

https://github.com/dlang/phobos/blob/17b1a11afd74f9f8a69af93d77d4548a557e1b89/std/container/array.d#L137

-Steve