opIndexUnary post in-/decrement how to ?

[Tejas]

On Wednesday, 14 July 2021 at 11:31:36 UTC, Tejas wrote:
> On Wednesday, 14 July 2021 at 10:07:38 UTC, wjoe wrote:
>> I'm want to do something like this
>> ```D
>> part_int_t!(1,2,3) i;
>>
>> auto x = -i[0];
>> --i[1]; // 1
>> i[1]++; // 2
>>
>> ```
>> I think the operator I need to overload would be opIndexUnary 
>> which I did.
>> (1) compiles.
>> (2) doesn't - the compiler complains that i.opIndex isn't an 
>> lvalue and can't be modified.
>> The language spec says that Post in- and decrement are 
>> rewritten but something's fishy.
>> What's going on behind the scene and how can I make it work?
>
> Please check the language spec here:
>
> https://dlang.org/spec/operatoroverloading.html#postincrement_postdecrement_operators
>
> You can't directly overload the postincrement operator.
>
> You need to rewrite it like:
>
> ``` {auto a = i[1] , ++i[1] , a} //note the , not the ;```
>
> Sorry I can't provide something even more concrete.

Ignore this, I wanted to say that this is what the _compiler_ 
rewrites it to when _you_ write ```i[1]++```

There is no way to explicitly overload the ```post increment``` 
operator because of this.