Re: [boost] Is Boost.Range broken?

Subject: Re: [boost] Is Boost.Range broken?
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2008-11-22 12:13:45

Andrey Semashev wrote:

> Yes, in general default-constructed
> iterators are singular and they cannot be used reliably. However, not all
> iterators behave that way. Pointers, for example, are NULL on
> default-initialization (which is used in the default constructor of the
> iterator_range class). I can well have my own iterators that are
> default-constructible and allow comparison in this state. And I don't
> understand why an iterator range of these iterators suddenly restricts me
> from being able to compare these iterators in empty(), for example.

Iterators where default-construction leads to a valid past-the-end 
iterator for all sequences are a fairly special case of iterators, even 
if they happen to be quite common.
However, that is certainly not guaranteed by the iterator concepts. 
Therefore, when you deal with iterators in a generic way, you should not 
assume such a thing.

iterator_range being a generic tool, it wants to maintain the invariants 
which are necessary to make it work whatever its parameters are, even if 
those invariants happen not to be necessary for some parameters.

Maybe if your iterators are so peculiar and you want to be able to rely 
on that property, you should use something else than iterator_range 
which is designed for all iterators.