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3188. istreambuf_iterator::pointer should not be unspecified

Section: 24.6.4 [istreambuf.iterator] Status: New Submitter: Jonathan Wakely Opened: 2019-02-21 Last modified: 2019-10-30

Priority: 3

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Discussion:

The current working paper requires iterator_traits<Iter>::pointer to be void if Iter doesn't define operator-> (24.3.2.3 [iterator.traits]). We recently removed operator-> from istreambuf_iterator via LWG 2790(i), therefore either its pointer member should be void, or there should be a partial specialization of iterator_traits. Do we want to change unspecified to void in the class synopsis in [istreambuf.iterator]?

[2019-03-03, Daniel provides concrete wording]

[2019-03-05 Priority set to 3 after reflector discussion]

[2019-03-05, Daniel comments]

With the acceptance of P1252R2 the committee decided to deprecate operator-> of move_iterator, interestingly without mentioning what should happen with its current pointer typedef (which is equal to the template parameter Iterator and thus never void). Effectively this is a very similar situation as for the here discussed istreambuf_iterator case and it seems attractive to me to solve both cases similarly.

[2019-10-30, Jonathan comments]

Also, reverse_iterator::operator->() is now constrained and so not always defined, but reverse_iterator::pointer is defined unconditionally.

Proposed resolution:

This wording is relative to N4800.

  1. Change class template istreambuf_iterator synopsis, 24.6.4 [istreambuf.iterator], as indicated:

    template<class charT, class traits = char_traits<charT>>
class istreambuf_iterator {
public:
  using iterator_category = input_iterator_tag;
  using value_type        = charT;
  using difference_type   = typename traits::off_type;
  using pointer           = voidunspecified;
  using reference         = charT;
  […]
};