Re: [boost] AlRangeExandrescu?

Subject: Re: [boost] AlRangeExandrescu?
From: Andrei Alexandrescu (andrei_at_[hidden])
Date: 2009-07-24 19:50:34

Rogier van Dalen wrote:
> On Thu, Jul 23, 2009 at 13:48, David Abrahams<dave_at_[hidden]> wrote:
>> Hi Neil,
>>
>> I'm sure someone already spoke to you about this, but just in case: Andrei
>> Alexandrescu gave a very interesting presentation at BoostCon that was based
>> on a "ranges only" approach that should eliminate issues like this one:
> 
> That looks very interesting. Is there any documentation on this out
> there? I found the slides:
> 
> http://www.boostcon.com/site-media/var/sphene/sphwiki/attachment/2009/05/08/iterators-must-go.pdf
> 
> and documentation for a D implementation:
> http://www.digitalmars.com/d/2.0/phobos/std_algorithm.html
> http://www.digitalmars.com/d/2.0/phobos/std_range.html
> 
> I'm wondering why "popFront()" is mutable and edits the range rather
> than return a range without the first element. The latter might allow
> compile-time heterogeneous sequences (like boost::fusion::vector) to
> conform to this range concept as well. I just realised you could then
> write a foreach function that works on both homogeneous and
> heterogeneous sequences basically like:
> 
> template <class Range, class Function>
> void foreach (Range range, Function function)
> {
>     if (!range.empty())
>     {
>         function (range.front());
>         foreach (range.popFront(), function);
>     }
> }
> 
> Is popFront() mutable just for efficiency? Or is there something else
> I'm missing?

It's only efficiency. I was very attracted to popFront returning the new 
range (100% functional interface!) but I gave up for efficiency reasons. 
I didn't want iteration with ranges to be cool and iteration with other 
means to be efficient.

Andrei