24 Ranges library [ranges]

24.6 Range factories [range.factories]

24.6.3 Iota view [range.iota]

24.6.3.3 Class iota_­view​::​iterator [range.iota.iterator]

namespace std::ranges {
  template<weakly_incrementable W, semiregular Bound>
    requires weakly-equality-comparable-with<W, Bound>
  struct iota_view<W, Bound>::iterator {
  private:
    W value_ = W();             // exposition only
  public:
    using iterator_concept = see below;
    using iterator_category = input_iterator_tag;
    using value_type = W;
    using difference_type = IOTA-DIFF-T(W);

    iterator() = default;
    constexpr explicit iterator(W value);

    constexpr W operator*() const noexcept(is_nothrow_copy_constructible_v<W>);

    constexpr iterator& operator++();
    constexpr void operator++(int);
    constexpr iterator operator++(int) requires incrementable<W>;

    constexpr iterator& operator--() requires decrementable<W>;
    constexpr iterator operator--(int) requires decrementable<W>;

    constexpr iterator& operator+=(difference_type n)
      requires advanceable<W>;
    constexpr iterator& operator-=(difference_type n)
      requires advanceable<W>;
    constexpr W operator[](difference_type n) const
      requires advanceable<W>;

    friend constexpr bool operator==(const iterator& x, const iterator& y)
      requires equality_comparable<W>;

    friend constexpr bool operator<(const iterator& x, const iterator& y)
      requires totally_ordered<W>;
    friend constexpr bool operator>(const iterator& x, const iterator& y)
      requires totally_ordered<W>;
    friend constexpr bool operator<=(const iterator& x, const iterator& y)
      requires totally_ordered<W>;
    friend constexpr bool operator>=(const iterator& x, const iterator& y)
      requires totally_ordered<W>;
    friend constexpr auto operator<=>(const iterator& x, const iterator& y)
      requires totally_ordered<W> && three_way_comparable<W>;

    friend constexpr iterator operator+(iterator i, difference_type n)
      requires advanceable<W>;
    friend constexpr iterator operator+(difference_type n, iterator i)
      requires advanceable<W>;

    friend constexpr iterator operator-(iterator i, difference_type n)
      requires advanceable<W>;
    friend constexpr difference_type operator-(const iterator& x, const iterator& y)
      requires advanceable<W>;
  };
}
1
#
iterator​::​iterator_­concept is defined as follows:
  • (1.1)
    If W models advanceable, then iterator_­concept is random_­access_­iterator_­tag.
  • (1.2)
    Otherwise, if W models decrementable, then iterator_­concept is bidirectional_­iterator_­tag.
  • (1.3)
    Otherwise, if W models incrementable, then iterator_­concept is forward_­iterator_­tag.
  • (1.4)
    Otherwise, iterator_­concept is input_­iterator_­tag.
2
#
[ Note
:
Overloads for iter_­move and iter_­swap are omitted intentionally.
— end note
 ]
🔗
constexpr explicit iterator(W value);
3
#
Effects: Initializes value_­ with value.
🔗
constexpr W operator*() const noexcept(is_nothrow_copy_constructible_v<W>);
4
#
Effects: Equivalent to: return value_­;
5
#
[ Note
:
The noexcept clause is needed by the default iter_­move implementation.
— end note
 ]
🔗
constexpr iterator& operator++();
6
#
Effects: Equivalent to: 
++value_;
return *this;
🔗
constexpr void operator++(int);
7
#
Effects: Equivalent to ++*this.
🔗
constexpr iterator operator++(int) requires incrementable<W>;
8
#
Effects: Equivalent to: 
auto tmp = *this;
++*this;
return tmp;
🔗
constexpr iterator& operator--() requires decrementable<W>;
9
#
Effects: Equivalent to: 
--value_;
return *this;
🔗
constexpr iterator operator--(int) requires decrementable<W>;
10
#
Effects: Equivalent to: 
auto tmp = *this;
--*this;
return tmp;
🔗
constexpr iterator& operator+=(difference_type n) requires advanceable<W>;
11
#
Effects: Equivalent to: 
if constexpr (is-integer-like<W> && !is-signed-integer-like<W>) {
  if (n >= difference_type(0))
    value_ += static_cast<W>(n);
  else
    value_ -= static_cast<W>(-n);
} else {
  value_ += n;
}
return *this;
🔗
constexpr iterator& operator-=(difference_type n) requires advanceable<W>;
12
#
Effects: Equivalent to: 
if constexpr (is-integer-like<W> && !is-signed-integer-like<W>) {
  if (n >= difference_type(0))
    value_ -= static_cast<W>(n);
  else
    value_ += static_cast<W>(-n);
} else {
  value_ -= n;
}
return *this;
🔗
constexpr W operator[](difference_type n) const requires advanceable<W>;
13
#
Effects: Equivalent to: return W(value_­ + n);
🔗
friend constexpr bool operator==(const iterator& x, const iterator& y) requires equality_comparable<W>;
14
#
Effects: Equivalent to: return x.value_­ == y.value_­;
🔗
friend constexpr bool operator<(const iterator& x, const iterator& y) requires totally_­ordered<W>;
15
#
Effects: Equivalent to: return x.value_­ < y.value_­;
🔗
friend constexpr bool operator>(const iterator& x, const iterator& y) requires totally_­ordered<W>;
16
#
Effects: Equivalent to: return y < x;
🔗
friend constexpr bool operator<=(const iterator& x, const iterator& y) requires totally_­ordered<W>;
17
#
Effects: Equivalent to: return !(y < x);
🔗
friend constexpr bool operator>=(const iterator& x, const iterator& y) requires totally_­ordered<W>;
18
#
Effects: Equivalent to: return !(x < y);
🔗
friend constexpr auto operator<=>(const iterator& x, const iterator& y) requires totally_­ordered<W> && three_­way_­comparable<W>;
19
#
Effects: Equivalent to: return x.value_­ <=> y.value_­;
🔗
friend constexpr iterator operator+(iterator i, difference_type n) requires advanceable<W>;
20
#
Effects: Equivalent to: return i += n;
🔗
friend constexpr iterator operator+(difference_type n, iterator i) requires advanceable<W>;
21
#
Effects: Equivalent to: return i + n;
🔗
friend constexpr iterator operator-(iterator i, difference_type n) requires advanceable<W>;
22
#
Effects: Equivalent to: return i -= n;
🔗
friend constexpr difference_type operator-(const iterator& x, const iterator& y) requires advanceable<W>;
23
#
Effects: Equivalent to: 
using D = difference_type;
if constexpr (is-integer-like<W>) {
  if constexpr (is-signed-integer-like<W>)
    return D(D(x.value_) - D(y.value_));
  else
    return (y.value_ > x.value_)
      ? D(-D(y.value_ - x.value_))
      : D(x.value_ - y.value_);
} else {
  return x.value_ - y.value_;
}