[Boost-users] Re: boost::iterator_facade problem with postfix increment proxy

Jens Theisen writes:

David Abrahams wrote:

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Jens Theisen writes:

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My reference type is a simple reference, I want to implement an lvalue iterator (at least in some cases). And why is it only single-pass?

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I am trying to make a proxy iterator ^^^^^^^^^^^^^^ What do you mean by that?

It is a class templated on a value_type to with implementations can be attached (at run time). For example:

List< char > l = makeList(some_std_string) + makeList(some_char_array);

l.begin(), l.end() give you an iterator which type depends solely on the value_type (char in this case), rather than the iterator types used as backends (std::string::iterator and pointers). These iterators will iterate over the std::string first and after this over the char array.

We call that "any_iterator" (see http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl?LibrariesUnde...)

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I don't see why that would be incompatible with forward traversal. We don't even seem to have a requirement that a copy of an iterator compares equal with it. Perhaps we should; then you might be in trouble [Jeremy, Thomas, your thoughts?]

Oh, you're right. I somehow assumed that would be the case. However, this is a requirement for Forward iterators, and iterator_faced gives the forward_traversal_tag to Forward traversal iterators with reference reference type. So it maybe a good idea to add this requirement.

Yeah, I agree.

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That shouldn't be slow if there's plenty of inlining.

The indirections are runtime indirections.

I see. Well, a generalized single-pass iterator can't be writable unless it has a proxy reference, IIRC. Otherwise, how does *x = a; work? -- Dave Abrahams Boost Consulting www.boost-consulting.com