rectifiedIndexOf()

[Basile B.]

On Friday, 5 May 2023 at 00:19:01 UTC, Salih Dincer wrote:
> It has a traditional very beautiful function:  indexOf() but it 
> has an important problem: returns -1 when it can't find 'c'...
>
> ```d
> void main()
> {
>   enum chr = 'c';
>   auto arr = "dlang".dup;
>   if(auto res = arr.indexOf(chr))
>   {
>     assert(arr[res] == chr);
>     // core.exception.ArrayIndexError
>   }
> }
> ```
>
> When you try to solve the problem with boolean logic, res is 
> now a bool.
> [...]
> So now that we've broken the traditional index approach, you 
> need to consider this (res - 1) in your code.
>
> SDB at 79

As often in D you can use a struct to help:

```d
auto toBool(ptrdiff_t t)
{
     struct ToBool
     {
         ptrdiff_t value;

         alias value this;

         bool opCast(T : bool)()
         {
             return value != -1;
         }
     }
     return ToBool(t);
}

void main()
{
       enum chr = 'l';
       auto arr = "dlang".dup;
       if (auto res = arr.indexOf(chr).toBool())
       {
             assert(res == 1);
       }
}
```

`opCast` is used for the `if` condition and the original value 
for reading back in the array, via `alias this`.