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

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iota_view::iota_view
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iota_view ( ) requires std:: default_initializable < W > = default ;
(1) (since C++20)
constexpr explicit iota_view ( W value ) ;
(2) (since C++20)
constexpr explicit iota_view ( std:: type_identity_t < W > value,
std:: type_identity_t < Bound > bound ) ;
(3) (since C++20)
constexpr explicit iota_view ( /*iterator*/ first, /* see below */ last ) ;
(4) (since C++20)

Constructs an iota_view .

Overload Data members
value_ bound_
(1) value-initialized value-initialized
(2) initialized with value
(3) initialized with bound
(4) initialized with first. value_ see below
2,3) If any of the following conditions is satisfied, the behavior is undefined:
4) If any of the following conditions is satisfied, the behavior is undefined:
The type of last and the method of initializing bound_ are determined by the type Bound denotes:
The type Bound denotes The type of last bound_
W iterator initialized with last. value_
std::unreachable_sentinel_t Bound initialized with last
any other type sentinel initialized with last. bound_

Parameters

value - the starting value
bound - the bound
first - the iterator denoting the starting value
last - the iterator or sentinel denoting the bound

Example

Run this code 
#include <cassert>
#include <iostream>
#include <iterator>
#include <ranges>
 
int main()
{
    const auto l = {1, 2, 3, 4};
 
    auto i1 = std::ranges::iota_view<int, int>(); // overload (1)
    assert(i1.empty() and i1.size() == 0);
 
    auto i2 = std::ranges::iota_view(1); // overload (2)
    assert(not i2.empty() and i2.front() == 1);
    for (std::cout << "1) "; auto e : i2 | std::views::take(3))
        std::cout << e << ' ';
    std::cout << '\n';
 
    auto i3 = std::ranges::iota_view(std::begin(l)); // overload (2)
    assert(not i3.empty() and i3.front() == l.begin());
    for (std::cout << "2) "; auto e : i3 | std::views::take(4))
        std::cout << *e << ' ';
    std::cout << '\n';
 
    auto i4 = std::ranges::iota_view(1, 8); // overload (3)
    assert(not i4.empty() and i4.front() == 1 and i4.back() == 7);
    for (std::cout << "3) "; auto e : i4)
        std::cout << e << ' ';
    std::cout << '\n';
 
    auto i5 = std::ranges::iota_view(l.begin(), l.end()); // overload (4)
    for (std::cout << "4) "; auto e : i5)
        std::cout << *e << ' ';
    std::cout << '\n';
 
    auto i6 = std::ranges::iota_view(l.begin(), std::unreachable_sentinel); // (4)
    for (std::cout << "5) "; auto e : i6 | std::views::take(3))
        std::cout << *e << ' ';
    std::cout << '\n';
}

Output: 

1) 1 2 3
2) 1 2 3 4
3) 1 2 3 4 5 6 7
4) 1 2 3 4
5) 1 2 3

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 3523 C++20 overload (4) might use wrong sentinel type corrected
P2711R1 C++20 overloads (3,4) were not explicit made explicit
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