Super-dee-duper D features

[Andrei Alexandrescu (See Website For Email)]

Kirk McDonald wrote:
> Sean Kelly wrote:
>> Derek Parnell wrote:
>>
>>> On Tue, 13 Feb 2007 17:39:46 +0100, Frits van Bommel wrote:
>>>
>>>> Andrei Alexandrescu (See Website For Email) wrote:
>>>>
>>>>> Bill Baxter wrote:
>>>>>
>>>>>> Yeh, I don't get it either.  How would that help me implement 
>>>>>> merge() from merge sort for instance?
>>>>>
>>>>> Merge bumps the iteration in both collections conditionally. The 
>>>>> form above bumps the iteration in the two collections 
>>>>> unconditionally, until one is finished; then it continues with the 
>>>>> other until that is finished.
>>>>
>>>> In other words, it doesn't :(.
>>>
>>>
>>> I imaging that the full syntax will also include this form ...
>>>
>>>   foreach (int x, i ; coll1) (int y, j ; coll2)   {
>>>    ... use i and j ...
>>>      if (somecondition)
>>>         x = ...  // To set the index back or forward to some
>>>                  // arbitary point in the array 'coll1'.
>>>   }
>>
>>
>> This currently works for built-in arrays but not for user-defined 
>> types.  Also, I think the fact that it works as all is the result of 
>> an implementation detail, not spec-defined behavior.
>>
>>
>> Sean
> 
> There's no reason a user-defined type couldn't implement this.

Exactly. Walter and I have bounced a couple of possibilities and 
concluded that the feature is of "medium difficulty/medium usefulness". 
Probably Walter will look into implementing this first:

foreach (i ; 0 .. n)
{
   ...
}


Andrei