Difference between revisions of "cpp/ranges/iota view"

Revision as of 08:58, 29 January 2024

Customization point objects

The name views::iota denotes a customization point object, which is a const function object of a literal semiregular class type. For exposition purposes, the cv-unqualified version of its type is denoted as __iota_fn.

All instances of __iota_fn are equal. The effects of invoking different instances of type __iota_fn on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, views::iota can be copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to views::iota above, __iota_fn models

• std::invocable<__iota_fn, Args...>,
• std::invocable<const __iota_fn, Args...>,
• std::invocable<__iota_fn&, Args...>, and
• std::invocable<const __iota_fn&, Args...>.
  

Otherwise, no function call operator of __iota_fn participates in overload resolution.

Data members

Member functions

Deduction guides

For any type T, /* is-integer-like */<T> is true if and only if T is integer-like, and /* is-signed-integer-like */<T> is true if and only if T is integer-like and capable of representing negative values.

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

Helper templates

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

Example

#include <algorithm>
#include <iostream>
#include <ranges>
 
struct Bound
{
    int bound;
    bool operator==(int x) const { return x == bound; }
};
 
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, Bound{10}))
        std::cout << i << ' ';
    std::cout << '\n';
 
    for (int i : std::views::iota(1) | std::views::take(9))
        std::cout << i << ' ';
    std::cout << '\n';
 
    std::ranges::for_each(std::views::iota(1, 10), [](int i)
    {
        std::cout << i << ' ';
    });
    std::cout << '\n';
}

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Defect reports

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

See also