Super-dee-duper D features

[kris]

Bill Baxter wrote:
> kris wrote:
> 
>> Bill Baxter wrote:
>>
>>> kris wrote:
>>>
>>>> kris wrote:
>>>>
>>>>> Bill Baxter wrote:
>>>>>
>>>>>> Frits van Bommel wrote:
>>>>>>
>>>>>>> By the way, would the new loop syntax allow more than two 
>>>>>>> collections to be simultaneously iterated?
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Whoa!  I certainly hope so.  It hadn't even occurred to me that 
>>>>>> Andrei might mean this syntax can only be used for just two 
>>>>>> collections.  If that's the case then ... ick.
>>>>>>
>>>>>> --bb
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> InterleavedIterator does multiple collections via using multiple 
>>>>> instances of InterleavedIterator. It's simple to use, and only 
>>>>> needs to be written once. Would be better to implement some basic 
>>>>> iterator needs than to introduce some tricky new syntax?
>>>>>
>>>>> - Kris
>>>>
>>>>
>>>>
>>>>
>>>> Should have given an example. Simple case with 2 entities:
>>>>
>>>> auto two = InterleavedInterator (x, y);
>>>> foreach (x; two) ...
>>>>
>>>> more than 2:
>>>>
>>>> auto three = InterleavedInterator (two, z);
>>>> foreach (x; three) ...
>>>
>>>
>>>
>>> Should have also mentioned where one can find this mythical 
>>> InterleavedIterator.
>>>
>>> --bb
>>
>>
>> There is no 'standard' one at this time that I know of (judging by the 
>> discussion on it a while back). However, Tango does have this beastie 
>> in the collections package. The point is, coming up with a lightweight 
>> core Iterator approach would likely provide a simpler and more 
>> dependable solution.
> 
> 
> Ok that wasn't clear to me.  It sounded like you were talking about code 
> I could type in today and have it work given suitable (but not 
> specified) imports.
> 
>> in the above example, x, y, and z are all iterators themselves. If D 
>> had a core notion of Iterator, that's what those would be. For 
>> instance, D iterators might map to a delegate (which is what the body 
>> of a foreach actually is).
> 
> 
> Yeh, basically it's the same as the Python izip that mentioned.  That's 
> python's name for InterleavedIterator.
> 
> I think the issue with D right now is that the 'x' returned by a 
> hypothetical InterleavedIterator would ideally be a tuple.  And you 
> would access the elements with x[0],x[1],x[2] (int the 'three' case 
> above).  Or you could do  foreach(x,y,z; three) and have it unpacked for 
> you.
> 
> I think it would be great if this kind of stuff worked.  I'm much less 
> excited about a built-in syntax that _only_ knows how to do that one trick.
> 
> --bb


Why would it return a tuple? Would the collection content be of 
differing types? If not, then the InterleavedIterator would likely have 
an opApply() for use in the foreach? That's how the Tango one operates, 
fwiw.