Reading about D: few questions

[Timon Gehr]

On 12/24/2011 07:00 PM, Andrew Wiley wrote:
> On Sat, Dec 24, 2011 at 9:50 AM, Timon Gehr<timon.gehr at gmx.ch>  wrote:
>> On 12/24/2011 06:18 PM, Andrew Wiley wrote:
>>>
>>> 2011/12/24 Mr. Anonymous<mailnew4ster at gmail.com>:
>>>
>>>> On 24.12.2011 19:01, Denis Shelomovskij wrote:
>>>>>
>>>>>
>>>>> 23.12.2011 22:51, bearophile пишет:
>>>>>>>
>>>>>>>
>>>>>>> ++a[] works, but a[]++ doesn't.
>>>>>>
>>>>>>
>>>>>> Already known compiler bug.
>>>>>
>>>>>
>>>>>
>>>>> Is it a joke? Array expression in D are for performance reasons to
>>>>> generate x2-x100 faster code without any compiler optimisations. Link to
>>>>> one of these epic comments (even x100 more epic because of '%' use
>>>>> instead of 'x###'):
>>>>>
>>>>>
>>>>> https://github.com/D-Programming-Language/druntime/blob/master/src/rt/arraybyte.d#L1127
>>>>>
>>>>>
>>>>> But `a[]++` should store a copy of `a`, increment elements and return
>>>>> stored copy. It is hidden GC allocation. We already have a silent
>>>>> allocation in closures, but here a _really large_ peace of data can be
>>>>> allocated. Yes, this allocation sometimes can be optimized out but not
>>>>> always.
>>>>>
>>>>> IMHO, D should not have `a[]++` operator.
>>>>
>>>>
>>>>
>>>> Why should it store a copy? o_O
>>>> I also don't see any allocations in the code on the URL above.
>>>
>>>
>>> int a_orig = a++;
>>> int[] arr_orig = arr[]++;
>>>
>>> If ++ is going to be applied to an array, it needs to have the same
>>> meaning as it does elsewhere. After this operation, arr_orig and arr
>>> must refer to different arrays for that to be true.
>>
>>
>> Not necessarily.
>>
>> class D{
>>     int payload;
>>     D opUnary(string op:"++")(){payload++; return this;}
>> }
>>
>> void main() {
>>     D d = new D;
>>     assert(d.payload == 0);
>>     assert(d++.payload == 1);
>> }
>
> That doesn't match integer semantics:
> int a = 0;
> assert(a++ == 0);
> assert(a == 1);

Yes, that was my point.