opIndexUnary post in-/decrement how to ?

[Tejas]

On Wednesday, 14 July 2021 at 13:09:56 UTC, vit wrote:
> On Wednesday, 14 July 2021 at 12:49:58 UTC, Tejas wrote:
>> 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);
>> }
>>
>> ```
>
> From doc: https://dlang.org/spec/operatoroverloading.html
> Postincrement e++ and Postdecrement e-- Operators
> These are not directly overloadable, but instead are rewritten 
> in terms of the ++e and --e prefix operators:
>
> Postfix Operator Rewrites
> op	rewrite
> e--	(auto t = e, --e, t)
> e++	(auto t = e, ++e, t)
>
>
> Rewriting part doesn't work with operator overloading.

If the rewriting part doesn't work with overloading then why 
aren't we allowed to explicitly overload 
```post-increment/decrement``` operators?

How else will the OP solve their problem?

It must rewrite,  otherwise it's impossible (I think).