Re: [boost] Is Boost.Range broken?

Subject: Re: [boost] Is Boost.Range broken?
From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2008-11-26 09:15:55

Giovanni Piero Deretta skrev:
> On Wed, Nov 26, 2008 at 4:46 AM, Scott McMurray <me22.ca+boost_at_[hidden]> wrote:
>> On Tue, Nov 25, 2008 at 13:31, David Abrahams <dave_at_[hidden]> wrote:
>>> on Mon Nov 24 2008, "Tomas Puverle" <Tomas.Puverle-AT-morganstanley.com> wrote:
>>>
>>>>> There's no reason that they both have to be in boost. Boost range
>>>>> should let you use your own range class.
>>>> And you're absolutely right.  Having said that, it's not inconceivable that
>>>> others may have been relying on the same behavour.
>>>> That's one of the things this discussion was about.
>>> Yes.  The library maintainer ought to do something to help those people,
>>> by providing the old behavior in code somewhere (even if that code only
>>> appears in docs).
>>>
>> How about providing code something like this (thanks to Boost.Iterator):
>>
>>    template <class Iter>
>>    class nonsingular_default
>>      : public boost::iterator_adaptor<
>>            node_iter<Value>                // Derived
>>          , Iter                            // Base
>>        >
>>    {
>>     private:
>>        bool is_default_constructed;
>>
>>     public:
>>        node_iter()
>>          : node_iter::iterator_adaptor_(),
>>            is_default_constructed(true) {}
>>
>>        explicit node_iter(Iter i)
>>          : node_iter::iterator_adaptor_(i),
>>            is_default_constructed(false) {}
>>
>>     private:
>>        friend class boost::iterator_core_access;
>>        bool equal(nonsingular_default i) {
>>            if (is_default_constructed && i.is_default_constructed) {
>>                return true;
>>            }
>>            if (!is_default_constructed && !i.is_default_constructed) {
>>                return base == i.base();
>>            }
>>            return false;
>>        }
>>    };
>>
> 
> [ i think you want to change all node_iter to  nonsingular_default ]
> 
>> Allowing recovery of the old semantics using
>>
>>    iterator_range< nonsingular_default<I> >
>>
>> (at least for Tomas Puverle's use case.)
>>
>> This, of course, depends on the asserts getting removed, but that
>> behaviour is also replicable using the same technique.
> 
> I do not think you can even copy a singular iterator (and at least
> libstdc++ will assert in debug mode),

Right. you can't even copy a singular iterator (not portably, at least).

-Thorsten