Re: [boost] [iterator] Proposal to add is_const_iterator trait

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2007-05-12 19:24:55

----- Mensaje original -----
De: David Abrahams <dave_at_[hidden]>
Fecha: Domingo, Mayo 13, 2007 0:16 am
Asunto: Re: [boost] [iterator] Proposal to add is_const_iterator trait
Para: boost_at_[hidden]
> 
> on Sat May 12 2007, Andrey Semashev <andysem-AT-mail.ru> wrote:
[...]
> >
> > I apologize for returning to this, but as I'm reading the docs and
> > looking at my use cases I have before me I don't see how would I 
> > elide is_const_iterator when using iterator_adaptor. Suppose this:
> >
> >   template< typename ValueT >
> >   class MyList
> >   {
> >   public:
> >     typedef ValueT value_type;
> >
> >     // etc. all other common typedefs except iterators
> >
> >   private:
> >     struct MyNode
> >     {
> >       ValueT value;
> >       int m_SomeOtherData;
> >     };
> >     typedef std::list< MyNode > underlying_container;
> >
> >     template< typename >
> >     class MyIterator;
> >
> >   public:
> >     typedef MyIterator<
> >       typename underlying_container::iterator
> >     > iterator;
> >
> >     typedef MyIterator<
> >       typename underlying_container::const_iterator
> >     > const_iterator;
> >
> >   private:
> >     template< typename ItT >
> >     class MyIterator :
> >       public iterator_adaptor<
> >         MyIterator< ItT >,
> >         ItT,
> >         value_type,  // I have to substitute value type
> 
> No, just leave it out.  The default works.

I think this is the crux of the matter. value_type is *not*
the same type as underlying_container::value_type. I think
Andrey has a valid point here.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo