Re: [boost] Is Boost.Range broken?

Subject: Re: [boost] Is Boost.Range broken?
From: Scott McMurray (me22.ca+boost_at_[hidden])
Date: 2008-11-26 09:51:15

On Wed, Nov 26, 2008 at 09:15, Thorsten Ottosen
<thorsten.ottosen_at_[hidden]> wrote:
> Giovanni Piero Deretta skrev:
>>
>> On Wed, Nov 26, 2008 at 4:46 AM, Scott McMurray <me22.ca+boost_at_[hidden]>
>> wrote:
>>>
>>> [...]
>>
>> [ i think you want to change all node_iter to  nonsingular_default ]
>>

Yes, dumb copy-paste mistake on my part.

>>
>> 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).
>

Another good point.

I think this works, as the iterator_adaptor's copy ctr is never called:

   template <class Iter>
   class nonsingular_default
     : public boost::iterator_adaptor<
           nonsingular_default<Value>      // Derived
         , Iter                            // Base
       >
   {
    private:
       bool is_default_constructed;

    public:
       nonsingular_default()
         : nonsingular_default::iterator_adaptor_(),
           is_default_constructed(true) {}

       nonsingular_default(Iter const &i)
         : nonsingular_default::iterator_adaptor_(i),
           is_default_constructed(false) {}

       nonsingular_default(nonsingular_default const &i) {
           *this = i;
       }

       nonsingular_default &operator=(nonsingular_default const &i) {
           is_default_constructed = i.is_default_constructed;
           if (!is_default_constructed) {
               base_reference() = i.base();
           }
       }

    private:
       friend class boost::iterator_core_access;
       bool equal(nonsingular_default const &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;
       }
   };