Super-dee-duper D features

[Andrei Alexandrescu (See Website For Email)]

janderson wrote:
> Andrei Alexandrescu (See Website For Email) wrote:
>> renoX wrote:
>>> Andrei Alexandrescu (See Website For Email) a écrit :
>>>> James Dennett wrote:
>>>>> C++, of course, has std::for_each(e.begin(), e.end(), do_x);
>>>>> in its library (though that's weaker than it could be because
>>>>> of lack of support for convenient anonymous functions/lambdas).
>>>>>
>>>>> C++0x is very likely to have for(v: e).  It's implemented
>>>>> in ConceptGCC already. Java already has essentially that,
>>>>> as does C#.  This really doesn't set D apart (but at least
>>>>> D isn't falling behind here).
>>>>
>>>> BTW, D might soon have simultaneous iteration that will blow away 
>>>> all conventional languages:
>>>>
>>>> foreach (i ; coll1) (j ; coll2)
>>>> {
>>>>   ... use i and j ...
>>>> }
>>>> continue foreach (i)
>>>> {
>>>>   ... coll2 finished; use i ...
>>>> }
>>>> continue foreach (j)
>>>> {
>>>>   ... coll1 finished; use j ...
>>>> }
>>>>
>>>> Best languages out there are at best ho-hum when it comes about 
>>>> iterating through simultaneous streams. Most lose their elegant 
>>>> iteration statement entirely and come with something that looks like 
>>>> an old hooker early in the morning.
>>>
>>> At first, I really didn't like the 'continue foreach', then 
>>> afterwards I got used to it, I wonder if this is really such a 
>>> requested feature though, what's wrong with the good old 'for' or 
>>> 'while' for the complex case?
>>
>> Absolutely nothing's wrong. The same argument, however, could be 
>> formulated to render foreach redundant. We have for, don't we.
>>
>> The thing is foreach is terse and elegant and has a functional flavor 
>> that gives it safety and power that for doesn't have. It's only 
>> natural to ask oneself why all of these advantages must go away in a 
>> blink just because you want to iterate two things simultaneously.
>>
>>
>> Andrei
> 
> I think its about how much this feature will be used.  This one seems 
> like it could be useful but its pretty close to borderline-"feature for 
> feature sake" for me.  There are probably a lot of other features that 
> could be more useful then this one.

No doubt, but there are many factors to take into account (among which 
implementation difficulty). In Perl it's a constant source of friction 
for me. If I want to iterate through one thing (array, file, hash...), 
it's all dandy. As soon as I need to iterate over two things I need to 
import and use an arcane library, or fall back and use while(1) and do 
it all with the axe (which is what I end up doing most of the time).

I'm actually mildly surprised. Lately there was some talk around here 
about supporting the day-to-day programmers and so on. I find looping a 
very day-to-day thing, and looping over 2+ things at least a 
few-days-to-few-days thing. There is a need for parallel iteration, if 
nothing else shown by the existence of a library that addresses exactly 
that - to the extent possible in a library that's not in the position to 
control syntax, scoping, and visibility. I was sure people will be on 
this one like white on rice. But Bjarne Stroustrup was right: nobody 
knows what most programmers do :o).


Andrei