std::ranges::iota_view<W, Bound>::iterator

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struct /*iterator*/;
 (1) (exposition only*)
Helper alias templates
template< class I >
using /*iota-diff-t*/ = /* see below */;
 (2) (exposition only*)
Helper concepts
template< class I >

concept /*decrementable*/ =
    std::incrementable<I> && requires(I i) {
        { --i } -> std::same_as<I&>;
        { i-- } -> std::same_as<I>;

    };
 (3) (exposition only*)
template< class I >

concept /*advanceable*/ =
    /*decrementable*/<I> && std::totally_ordered<I> &&
    requires(I i, const I j, const /*iota-diff-t*/<I> n) {
        { i += n } -> std::same_as<I&>;
        { i -= n } -> std::same_as<I&>;
        I(j + n);
        I(n + j);
        I(j - n);
        { j - j } -> std::convertible_to</*iota-diff-t*/<I>>;

    };
 (4) (exposition only*)
1) ranges::iota_view<W, Bound>::iterator is the type of the iterators returned by begin() and end() of ranges::iota_view<W, Bound>.
2) Calculates the difference type for both iterator types and integer-like types.
  • If I is not an integral type, or if it is an integral type and sizeof(std::iter_difference_t<I>) is greater than sizeof(I), then /*iota-diff-t*/<I> is std::iter_difference_t<I>.
  • Otherwise, /*iota-diff-t*/<I> is a signed integer type of width greater than the width of I if such a type exists.
  • Otherwise, I is one of the widest integral types, and /*iota-diff-t*/<I> is an unspecified signed-integer-like type of width not less than the width of I. It is unspecified whether /*iota-diff-t*/<I> models weakly_incrementable in this case.
3) Specifies that a type is incrementable, and pre- and post- operator-- for the type have common meaning.
4) Specifies that a type is both decrementable and totally_ordered, and operator+=, operator-=, operator+, and operator- among the type and its different type have common meaning.

/*iterator*/ models

However, it only satisfies LegacyInputIterator if W models incrementable, and does not satisfy LegacyInputIterator otherwise.

Semantic requirements

3) Type I models decrementable only if I satisfies decrementable and all concepts it subsumes are modeled, and given equal objects a and b of type I:
  • If a and b are in the domain of both pre- and post- operator-- (i.e. they are decrementable), then the following are all true:
  • If a and b are in the domain of both pre- and post- operator++ (i.e. they are incrementable), then bool(--(++a) == b) is true.
4) Let D denote /*iota-diff-t*/<I>. Type I models advanceable only if I satisfies advanceable and all concepts it subsumes are modeled, and given
  • objects a and b of type I and
  • value n of type D,

such that b is reachable from a after n applications of ++a, all following conditions are satisfied:

  • (a += n) is equal to b.
  • std::addressof(a += n) is equal to std::addressof(a).
  • I(a + n) is equal to (a += n).
  • For any two positive values x and y of type D, if I(a + D(x + y)) is well-defined, then I(a + D(x + y)) is equal to I(I(a + x) + y).
  • I(a + D(0)) is equal to a.
  • If I(a + D(n - 1)) is well-defined, then I(a + n) is equal to [](I c) { return ++c; }(I(a + D(n - 1))).
  • (b += -n) is equal to a.
  • (b -= n) is equal to a.
  • std::addressof(b -= n) is equal to std::addressof(b).
  • I(b - n) is equal to (b -= n).
  • D(b - a) is equal to n.
  • D(a - b) is equal to D(-n).
  • bool(a <= b) is true.

Nested types

Type Definition
iterator_concept an iterator tag, see below
iterator_category
(only present if W models incrementable and
/*iota-diff-t*/<W> is an integral type) 		std::input_iterator_tag
value_type W
difference_type /*iota-diff-t*/<W>

Determining the iterator concept

iterator_concept is defined as follows:

Data members

Member Definition
W value_ the current value
(exposition-only member object*)

Member functions

std::ranges::iota_view::iterator::iterator

/*iterator*/() requires std::default_initializable<W> = default;
 (1) (since C++20)
constexpr explicit /*iterator*/( W value );
 (2) (since C++20)
1) Value initializes value_.
2) Initializes value_ with value.

std::ranges::iota_view::iterator::operator*

constexpr W operator*() const
    noexcept(std::is_nothrow_copy_constructible_v<W>);
 (since C++20)

Returns value_.

Example

Run this code
#include <cassert>
#include <ranges>
 
int main()
{
    auto it{std::views::iota(6, 9).begin()};
    const int& r = *it; // binds with temporary
    assert(*it == 6 and r == 6);
    ++it;
    assert(*it == 7 and r == 6);
}

std::ranges::iota_view::iterator::operator++

constexpr /*iterator*/& operator++();
 (1) (since C++20)
constexpr void operator++(int);
 (2) (since C++20)
constexpr /*iterator*/ operator++(int) requires std::incrementable<W>;
 (3) (since C++20)
1) Equivalent to ++value_ ; return *this;.
2) Equivalent to ++value_ ;.
3) Equivalent to auto tmp = *this; ++value_ ; return tmp;.

Example

Run this code
#include <cassert>
#include <ranges>
 
int main()
{
    auto it{std::views::iota(8).begin()};
    assert(*it == 8);
    assert(*++it == 9);
    assert(*it++ == 9);
    assert(*it == 10);
}

std::ranges::iota_view::iterator::operator--

constexpr /*iterator*/& operator--() requires /*decrementable*/<W>;
 (1) (since C++20)
constexpr /*iterator*/operator--(int) requires /*decrementable*/<W>;
 (2) (since C++20)
1) Equivalent to --value_ ; return *this;.
2) Equivalent to auto tmp = *this; --value_ ; return tmp;.

Example

Run this code
#include <cassert>
#include <ranges>
 
int main()
{
    auto it{std::views::iota(8).begin()};
    assert(*it == 8);
    assert(*--it == 7);
    assert(*it-- == 7);
    assert(*it == 6);
}

std::ranges::iota_view::iterator::operator+=

constexpr /*iterator*/& operator+=( difference_type n )
    requires /*advanceable*/<W>;
 (since C++20)

Updates value_ and returns *this:

Example

Run this code
#include <cassert>
#include <ranges>
 
int main()
{
    auto it{std::views::iota(5).begin()};
    assert(*it == 5);
    assert(*(it += 3) == 8);
}

std::ranges::iota_view::iterator::operator-=

constexpr /*iterator*/& operator-=( difference_type n )
    requires /*advanceable*/<W>;
 (since C++20)

Updates value_ and returns *this:

Example

Run this code
#include <cassert>
#include <ranges>
 
int main()
{
    auto it{std::views::iota(6).begin()};
    assert(*it == 6);
    assert(*(it -= -3) == 9);
}

std::ranges::iota_view::iterator::operator[]

constexpr W operator[]( difference_type n ) const
    requires /*advanceable*/<W>;
 (since C++20)

Returns W(value_ + n).

Example

Run this code
#include <cassert>
#include <ranges>
 
int main()
{
    auto it{std::views::iota(6).begin()};
    assert(*it == 6);
    assert(*(it + 3) == 9);
}

Non-member functions

operator==, <, >, <=, >=, <=>(std::ranges::iota_view::iterator)

friend constexpr bool operator==

    ( const /*iterator*/& x, const /*iterator*/& y )

    requires std::equality_comparable<W>;
 (1) (since C++20)
friend constexpr bool operator<

    ( const /*iterator*/& x, const /*iterator*/& y )

    requires std::totally_ordered<W>;
 (2) (since C++20)
friend constexpr bool operator>

    ( const /*iterator*/& x, const /*iterator*/& y )

    requires std::totally_ordered<W>;
 (3) (since C++20)
friend constexpr bool operator<=

    ( const /*iterator*/& x, const /*iterator*/& y )

    requires std::totally_ordered<W>;
 (4) (since C++20)
friend constexpr bool operator>=

    ( const /*iterator*/& x, const /*iterator*/& y )

    requires std::totally_ordered<W>;
 (5) (since C++20)
friend constexpr bool operator<=>

    ( const /*iterator*/& x, const /*iterator*/& y )

    requires std::totally_ordered<W> && std::three_way_comparable<W>;
 (6) (since C++20)
1) Returns x.value_ == y.value_.
2) Returns x.value_ < y.value_.
3) Returns y < x.
4) Returns !(y < x).
5) Returns !(x < y).
6) Returns x.value_ <=> y.value_.

The != operator is synthesized from operator==.

These functions are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when iterator is an associated class of the arguments.

operator+(std::ranges::iota_view::iterator)

friend constexpr /*iterator*/ operator+

    ( /*iterator*/ i, difference_type n )

    requires /*advanceable*/<W>;
 (1) (since C++20)
friend constexpr /*iterator*/ operator+

    ( difference_type n, /*iterator*/ i )

    requires /*advanceable*/<W>;
 (2) (since C++20)

Equivalent to i += n; return i;.

These functions are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when iterator is an associated class of the arguments.

operator-(std::ranges::iota_view::iterator)

friend constexpr /*iterator*/ operator-

    ( /*iterator*/ i, difference_type n )

    requires /*advanceable*/<W>;
 (1) (since C++20)
friend constexpr difference_type operator-

    ( const /*iterator*/& x, const /*iterator*/& y )

    requires /*advanceable*/<W>;
 (2) (since C++20)
1) Equivalent to i -= n; return i;.
2) Let D be difference_type:

These functions are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when iterator is an associated class of the arguments.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2259R1 C++20 member iterator_category is always defined defined only if W satisfies incrementable
LWG 3580 C++20 bodies of operator+ and operator- rule out implicit move made suitable for implicit move
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