David Abrahams wrote:
Vladimir Prus <ghost@cs.msu.su> writes:
And it seems to me, all single pass iterators have to store the value to allow for repeated operator*() calls.
Let's talk about concepts in the standard, i.e. input iterator.
Talking about input iterator, directory_iterator does not comply with *r++ requirement.
We invented single pass iterator; it can mean anything we say, and what we said doesn't imply that.
But it's the intention that new-style readable single-pass iterator is also a model of old-style input iterator? And the problem we're discussing is that directory_iterator is readable single-pass iterator but not input iterator? I see that std::input_iterator requirements say that after ++r any copies of the previous value of r are no longer required to be dereferencable. New iterators requirents are silent on this. Is this intentional? If single pass iterator requirements - would add the same note about ++r making iterators dereferencable - retain the same requirements for operator++(int) The result of r++ is not required even to be dereferencable, and *r++ is not required even to be to work for single-pass iterator, while it works for input iterators. The solutions I see are: 1) require that ++r does not makes any copies dereferencable, or 2) allow returning proxy from operator++(int) 3) require that result of r++ is dereferencable and is equivivalent to the dereferencing of the previous value of 'r'. The variant 2) would be most convenient for directory_iterator... - Volodya