Ranges and/versus iterators

[Jesse Phillips]

I think a good way to learn ranges is by looking at the interface to them, compared to those used by other languages. For one thing, C++ iterators are way more complicated than what you will find in many other languages; for example Java's iterator interface[1] is similar to a D range[2].

In both languages the interface is 3 functions (there are many types of ranges which require more, but only one kind of iterator).

Java:
bool hasNext()
E next()
void remove()

D:
bool empty()
E front()
void popFront()

These look almost identical but the semantics are very different. For example, hasNext() requires a look-ahead, while empty() does not. This is important since you may not be able to look ahead in a range.

next() performs the equivalent of calling front(); popFront(); And remove() has nothing to do with the iterator as it performs on the underlining collection.

Removing the look-ahead is probably one of the biggest improvements over Java's iterator.

1. http://java.sun.com/j2se/1.5.0/docs/api/java/util/Iterator.html
2. http://digitalmars.com/d/2.0/phobos/std_range.html#isInputRange

clueless bystander Wrote:

> Watching D evolve from the outside there seems to be a lot of ongoing discussion
> on this newsgroup about the D range idiom which is somehow opposed to conventional
> thinking about iterators.
> 
> Can someone please explain in plain words just exactly what a range is and how
> it differs from the iterator concept (if that's appropriate???) and what are the benefits
> from a data modeling and access perspective.
> 
> Sure, I'm clueless, though suspect many other bystanders would appreciate a
> succinct heads-up.
> 
> Thanks,
> clueless bystander