std::ranges::views::iota, std::ranges::iota_view

 

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Concepts library (C++20)

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Utilities library

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Ranges library (C++20)

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Technical Specifications

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range primitives
iterator_tsentinel_t	range_size_trange_difference_t	range_value_t	range_reference_trange_rvalue_reference_t
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Semiregular wrapper
Factories
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	views::counted
Adaptors
views::all_tviews::all join_viewviews::join take_viewviews::take basic_istream_viewistream_view	ref_view                                split_viewviews::split take_while_viewviews::take_while elements_viewviews::elements	common_viewviews::common transform_viewviews::transform drop_viewviews::drop keys_viewviews::keys	reverse_viewviews::reverse filter_viewviews::filter drop_while_viewviews::drop_while values_viewviews::values

 

template<std::weakly_incrementable W,          std::semiregular Bound = std::unreachable_sentinel_t>     requires __WeaklyEqualityComparableWith<W, Bound> && std::semiregular<W> class iota_view : public ranges::view_interface<iota_view<W, Bound>>	(1)	(since C++20)
namespace views {     inline constexpr /*unspecified*/ iota = /*unspecified*/; }	(2)	(since C++20)

1) A range factory that generates a sequence of elements by repeatedly incrementing an initial value. Can be both bounded and unbounded (infinite)

2) views::iota(E) and views::iota(E, F) are expression-equivalent to (has the same effect as) iota_view{E} and iota_view{E, F} respectively for any suitable subexpressions E and F

Expression-equivalent

Expression e is expression-equivalent to expression f, if e and f have the same effects, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

Helper templates

template<std::weakly_incrementable W, std::semiregular Bound> inline constexpr bool enable_borrowed_range<ranges::iota_view<W, Bound>> = true;

This specialization of std::ranges::enable_borrowed_range makes iota_view satisfy borrowed_range.

Data members

std::ranges::iota_view::base_

W value_ = W(); /* exposition-only */

the current value

std::ranges::iota_view::pred_

Bound bound_ = Bound(); /* exposition-only */

the bound (defaults to std::unreachable_sentinel_t)

Member functions

std::ranges::iota_view::iota_view

iota_view() = default;	(1)
constexpr explicit iota_view(W value);	(2)
constexpr iota_view(std::type_identity_t<W> value,                     std::type_identity_t<Bound> bound);	(3)

1) Default-initializes value_ and bound_

2) Initializes value_ with value and expects that Bound is either unreachable_sentinel_t (the default) or Bound() is reachable from value. This constructor is used to create unbounded iota views, e.g. iota(0) yields numbers 0,1,2..., infinitely.

3) Initializes value_ with value and bound_ with bound. This constructor is used to create bounded iota views, e.g. iota(10, 20) yields numbers from 10 to 19.

Parameters

value	-	the starting value
bound	-	the bound

std::ranges::iota_view::begin

constexpr iterator begin() const;

Returns the iterator initialized with value_

std::ranges::iota_view::end

constexpr auto end() const;	(1)
constexpr iterator end() const requires std::same_as<W, Bound>;	(2)

1) Returns the sentinel initialized with bound_ if this view is bounded, or std::unreachable_sentinel if this view is unbounded.

2) Returns the iterator initialized with bound_.

std::ranges::iota_view::size

constexpr auto size() const   requires (std::same_as<W, Bound> && __Advanceable<W>) ||            (std::integral<W> && std::integral<Bound>) ||              std::sized_sentinel_for<Bound, W> {   if constexpr (__is_integer_like<W> && __is_integer_like<Bound>)     return (value_ < 0)       ? ((bound_ < 0)         ? __make_unsigned_like(-value_) - __make_unsigned_like(-bound_)         : __make_unsigned_like(bound_) + __make_unsigned_like(-value_))       : __make_unsigned_like(bound_) - __make_unsigned_like(value_);   else     return __make_unsigned_like(bound_ - value_); }

Returns the size of the view if the view is bounded.

Deduction guides

template<class W, class Bound>     requires (!__is_integer_like<W> || !__is_integer_like<Bound> ||               __is_signed_integer_like<W> == __is_signed_integer_like<Bound>)   iota_view(W, Bound) -> iota_view<W, Bound>;

Note that the guide protects itself against signed/unsigned mismatch bugs, like views::iota(0, v.size()), where 0 is a (signed) int and v.size() is an (unsigned) std::size_t.

Nested classes

std::ranges::iota_view::iterator

template<class W, class Bound> struct iota_view<W, Bound>::iterator; /* exposition-only */

The return type of iota_view::begin.

This is a random_access_iterator if W models __Advanceable, a bidirectional_iterator if W models __Decrementable, a forward_iterator if W models incrementable, and input_iterator otherwise. However, it is only a LegacyInputIterator.

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

constexpr explicit iterator(W value);

Initializes exposition-only data member value_ with value. This value will be returned by operator* and incremented by operator++

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

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

returns the current value, by value (in other words, this is a read-only view)

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

constexpr iterator& operator++()	(1)
constexpr void operator++(int)	(2)
constexpr iterator operator++(int) requires std::incrementable<W>;	(3)

1) Equivalent to ++value_; return *this;

2) Equivalent to ++value_;

3) Equivalent to auto tmp = *this; ++value_; return tmp;

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

constexpr iterator& operator--() requires __Decrementable<W>;	(1)
constexpr iterator operator--(int) requires __Decrementable<W>;	(2)

1) Equivalent to --value_; return *this;

2) Equivalent to auto tmp = *this; --value_; return tmp;

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

constexpr W operator[](difference_type n) const requires __Advanceable<W>;

Equivalent to return W(value_ + n);

Other members as expected of an iterator.

std::ranges::iota_view::sentinel

template<class W, class Bound> struct iota_view<W, Bound>::sentinel; /* exposition-only */

The return type of iota_view::end.

std::ranges::iota_view::sentinel::bound_

Bound bound_ = Bound(); /* exposition only */

Exposition-only data member holding the sentinel (typically either a number, for a bounded iota view, or an instance of std::unreachable_sentinel_t for an unbounded iota view.

std::ranges::iota_view::sentinel::sentinel

sentinel() = default; constexpr explicit sentinel(Bound bound);

Initializes exposition-only data member bound_ with bound.

std::ranges::iota_view::sentinel::operator==

friend constexpr bool operator==(const iterator& x, const sentinel& y);

Equivalent to: x.value_ == y.bound_;.

std::ranges::iota_view::sentinel::operator-

friend constexpr std::iter_difference_t<W>     operator-(const iterator& x, const sentinel& y)     requires std::sized_sentinel_for<Bound, W>;	(1)
friend constexpr std::iter_difference_t<W>     operator-(const sentinel& x, const iterator& y)     requires std::sized_sentinel_for<Bound, W>;	(2)

1) Equivalent to return x.value_ - y.bound_;.

2) Equivalent to return -(y.value_ - x.bound_);.

Example

Run this code

#include <ranges>
#include <iostream>
 
int main()
{
    for (int i : std::ranges::iota_view{1, 10})
        std::cout << i << ' ';
    std::cout << '\n';
 
    for (int i : std::views::iota(1, 10))
        std::cout << i << ' ';
    std::cout << '\n';
 
    for (int i : std::views::iota(1) | std::views::take(9))
        std::cout << i << ' ';
    std::cout << '\n';
}

Output:

1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9