opIndexUnary post in-/decrement how to ?

[Tejas]

On Wednesday, 14 July 2021 at 12:35:07 UTC, wjoe wrote:
> On Wednesday, 14 July 2021 at 11:31:36 UTC, Tejas wrote:
>>
>> ``` {auto a = i[1] , ++i[1] , a} //note the , not the ;```
>>
>> Sorry I can't provide something even more concrete.
>
> Yes I saw that, and I suppose it would work just fine if it 
> were rewritten to just  ```++i[1]```.
> What I'm struggling to understand is the ```{auto a = i[1], ... 
> ,a}``` part. I can't parse that. What's up with the assignment 
> and the comma stuff ?

I think it's a bug, because the following works:

```d

import   std.stdio;

struct abc{
     int[100] a;
     int opIndex(int index){
         return a[index];
     }
     int opIndexUnary(string s)(int index)
         if(s == "++"){
         return ++a[index];
         }
     int[] opUnary(string s)() if (s == "++"){
         return a[] += 1;
     }
}

void main (){
     abc s;
     int[100] a;
     int temp;
     writeln (a[20]++);

     writeln(a[20]);

     writeln(++s[20]);

     writeln(s[20]);

     //writeln(s[0]++);// doesn't work for some reason

     writeln(s[0]);

     writeln(s++);//but this works!!

     writeln(s);
}

```