Reading about D: few questions

[Andrew Wiley]

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);