[Boost-users] Re: indirect_iterator of reverse_iterator

Thomas Matelich writes:

On Tue, 01 Mar 2005 12:55:21 -0500, David Abrahams wrote:

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Thomas Matelich writes:

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I'm a little behind the times and am trying to port my old iterator_adapters code to use the new library (1.32). We have a class which is little more than a wrapper around a vector, and I am having a heck of a time with setting its typedef for reverse_iterator and const_reverse_iterator. I just can't get const_reverse_iterator to do assignment and comparison with reverse_iterator.

I've tried to make indirect_iterators out of the native reverse iterators,

That almost certainly won't work, because the native reverse_iterator usually won't play nicely with the native const_reverse_iterator.

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using boost::reverse_iterators of indirect_iterators

What happens when you do that? (code, error messages) Have you verified that the const and mutable indirect_iterators interoperate the way you'd like?

So, of course, my sample application (attached) compiles just fine.

No it doesn't: vc-C++ c:\build\bin\tmp\foo.test\vc7.1\debug-python\threading-multi\foo.obj foo.cpp foo.cpp(255) : error C2662: 'TestItem::setItemKey' : cannot convert 'this' pointer from 'const boost::detail::add_pointer_impl<T>::no_ref_type' to 'TestItem &' with [ T=const boost::detail::iterator_facade_types::dereferenceable>::type>::type,boost::mpl::identityboost::random_access_traversal_tag::type,boost::mpl::identity::dereferenceable>::type >::type ,boost::iterator_difference::type>::value_type ] Conversion loses qualifiers But of course, you should have commented out the line that says:

c_r_iter->setItemKey(33,33); //does compile for new

Then it does compile just fine. Clearly you are doing something significantly different in your sample application.

In my failing version assigning a rev_iterator to a const_rev_iterator fails with the following error:

smartlisttest.cpp(352) : error C2440: 'initializing' : cannot convert from 'ZUtil::SmartList<T>::rev_iterator' to 'boost::reverse_iterator<Iterator>' with [ T=TestItem ] and [ Iterator=ZUtil::SmartList<TestItem>::const_iterator ] No constructor could take the source type, or constructor overload resolution was ambiguous

Well, it seems as though ZUtil::SmartList<TestItem>::rev_iterator and boost::reverse_iterator must not be the same type in your failing version. If the problem isn't immediately obvious, I suggest you run your code through the VC8 public beta. Jason Shirk, at my urging, implemented a fix to the error reporting that will unwind the typedefs in the error message so you can see what types are actually involved. -- Dave Abrahams Boost Consulting www.boost-consulting.com