Proposed resolution:

This wording is relative to N4659.

1. Add a new paragraph at the end of [iterator.requirements.general] as indicated:

   -12- An invalid iterator is an iterator that may be singular.(footnote: […])

   Iterators are called constexpr iterators if all defined iterator category operations, except a pseudo-destructor call ([expr.pseudo]) or the construction of an iterator with a singular value, are usable as constant expressions. [Note: For example, the types "pointer to int" and reverse_iterator<int*> are constexpr random access iterators. — end note]

   -13- In the following sections, a and b denote […]

2. Add a new paragraph at the end of [array.overview]:

   -3- An array satisfies all of the requirements of a container […]

   -?- iterator and const_iterator satisfy the constexpr iterator requirements ([iterator.requirements.general]).

[ 2018-06 Rapperswil Wednesday issues processing ]

This was resolved by P0858, which was adopted in Jacksonville.

[ 2017-11 Albuquerque Saturday issues processing ]

P0858R0 (adopted on Sat; to be moved in Jacksonville) will resolve this.

[ 2017-11 Albuquerque Thursday ]

It looks like 1581 is going to be resolved this week, so we should revisit soon.

[ 2017-11 Albuquerque Wednesday issue processing ]

Status to Open; We don't want to do this yet; gated on Core issue 1581 (affects swap). See also 2800.

Thomas to talk to Anthony about writing a paper detailing what it takes to be a constexpr iterator.

[ 2017-04-22, Antony Polukhin provides improved wording ]

[ 2017-03-04, Kona ]

Set priority to 2. Lisa and Alisdair to work with Antony to come up with better wording. The same wording can be used for 2938.

Previous resolution [SUPERSEDED]:

This wording is relative to N4640.

1. Add a new paragraph at the end of [array.overview]:

   -3- An array satisfies all of the requirements of a container […]

   -?- All operations on iterator and const_iterator that are required to satisfy the random access iterator requirements are usable in constant expressions.

[ 2017-03-02, Tim Song comments ]

I don't believe the blanket "all operations" wording is quite correct.

First, T t; (required by DefaultConstructible) isn't usable in a constant expression if the iterator is a pointer, since it would leave it uninitialized.

Second, an explicit destructor call u.~T() (required by Destructible) isn't usable if the iterator is a class type because it explicitly invokes a non-constexpr function (the destructor); see [expr.const]/2.2.

[ 2017-03-02, Kona ]

Wording tweaks suggested by LWG applied.

[ 2017-03-01, Kona ]

Antony Polukhin provides revised wording.

[ 2017-02-20 Marshall adds wording ]

I used the formulation "are literal types", rather than "shall be", since that denotes a requirement on the user.

Previous resolution [SUPERSEDED]:

This wording is relative to N4640.

1. Add a new paragraph at the end of [array.overview]:

   -?- iterator and const_iterator are literal types.

Force the literal type requirement for the iterator and const_iterator in the std::array so that iterators of std::array could be used in constexpr functions.

Proposed change: Add to the end of the [array.overview] section: iterator and const_iterator shall be literal types.