Re: [boost] AlRangeExandrescu?

Subject: Re: [boost] AlRangeExandrescu?
From: Andrei Alexandrescu (andrei_at_[hidden])
Date: 2009-07-28 17:20:29

Mathias Gaunard wrote:
> Andrei Alexandrescu wrote:
> 
>> Now here comes an interesting possibility. Boost::RangeEx also defines 
>> a typename Boost::RangeEx::iterator, and begin() and end() that return 
>> iterators. But it makes them optional! Meaning, as much as there are 
>> forward vs. bidirectional ranges, there are ranges that cloak 
>> iterators versus ranges that don't.
> 
> Would there be any reason for a range not to provide iterators except 
> those iterators being hard to write?
> 
> In case there is none, I don't think it's such a good idea to use 
> concept refining for a non conceptual difference, but rather an 
> implementation difficulty.

It's not only implementation difficulty. I have many ranges that make 
next no sense as iterators. For example I have a range that spits out 
random numbers. The notion is very easy to fathom as a range, but 
forcing it into the iterator framework would be forced for the designer 
as well as the user of the notion. The design would be a net loss for 
everybody if it were required to define an iterator.

Andrei