Bob Bell wrote:
Now consider a typical reverse loop, where we decrement backwards through [b, e):
while (b != e) { --e; // use *e; }
No "begin sentinel" is required to make this loop behave as expected. When b is created, it will point to the first element of the filtered pseudo-sequence; this means that eventually, e will become equal to b, and the loop will terminate.
Not if the filter predicate returns false for *b.
In fact, it seems that without a begin sentinel, uses of b and e are just as well-defined (or undefined) as equivalent ordinary iterators. For example, for an ordinary sequence [b, e), --b is well-defined only if there is something dereferencable there. For a filter iterator lacking a begin sentinel, the same thing is true.
What do you think?
I think you overlooked something important. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com