NAME¶

std::ranges::in_fun_result - std::ranges::in_fun_result

Synopsis¶

Defined in header <algorithm>
template< class I, class F > (since C++20)
struct in_fun_result;

ranges::in_fun_result is a class template that provides a way to store an iterator
and a function object as a single unit.

This class template has no base classes or declared members other than those shown
below. Thus it is suitable for use with structured bindings.

All special member functions of this class template are implicitly declared, which
makes specializations be aggregate classes, and propagate triviality,
potentially-throwing-ness, and constexpr-ness of corresponding operations on data
members.

Template parameters¶

I - the type of the iterator that the ranges::in_fun_result stores.
F - the type of the function object that the ranges::in_fun_result stores.

Data members

Member name Definition
in a value (that is supposed to be an iterator) of type I.
(public member object)
fun a value (that is supposed to be a function object) of type F.
(public member object)

All these members are declared with [[no_unique_address]] attribute.

Member functions¶

std::ranges::in_fun_result::operator in_fun_result<I2, F2>

template<class I2, class F2>

requires std::convertible_to<const I&, I2> && std::convertible_to<const F&, F2> (1)

constexpr operator in_fun_result<I2, F2>() const &;
template<class I2, class F2>

requires std::convertible_to<I, I2> && std::convertible_to<F, F2> (2)

constexpr operator in_fun_result<I2, F2>() &&;

Converts *this to the result by constructing every data member of the result from
the corresponding member of *this.

1) Equivalent to return {in, fun};.
2) Equivalent to return {std::move(in), std::move(fun)};.

Standard library¶

The following standard library functions use ranges::in_fun_result as the return
type:

Algorithm functions
ranges::for_each applies a function to a range of elements
(C++20) (niebloid)
ranges::for_each_n applies a function object to the first N elements of a sequence
(C++20) (niebloid)

Synopsis¶

namespace std::ranges
{
template<class I, class F>
struct in_fun_result
{
[[no_unique_address]] I in;
[[no_unique_address]] F fun;

template<class I2, class F2>
requires std::convertible_to<const I&, I2> && std::convertible_to<const F&, F2>
constexpr operator in_fun_result<I2, F2>() const &
{
return {in, fun};
}

template<class I2, class F2>
requires std::convertible_to<I, I2> && std::convertible_to<F, F2>
constexpr operator in_fun_result<I2, F2>() &&
{
return {std::move(in), std::move(fun)};
}
};
}

Notes¶

Each standard library algorithm that uses this family of return types declares a new
alias type, e.g. using merge_result = in_in_out_result<I1, I2, O>;.

The names for such aliases are formed by adding the suffix "_result" to the
algorithm's name. So, the return type of std::ranges::merge can be named as
std::ranges::merge_result.

Unlike std::pair and std::tuple, this class template has data members of meaningful
names.

Example¶

// Run this code

#include <algorithm>
#include <cassert>
#include <iostream>
#include <iterator>
#include <ranges>

int main()
{
int v[]{1, 2, 3};

const std::ranges::in_fun_result res1 = std::ranges::for_each_n(
v, std::size(v),
[](int& x) { return x = -x; } // negating lambda
);
assert(res1.in == std::end(v));

const std::ranges::in_fun_result res2 = std::ranges::for_each(
std::begin(v),
res1.in,
[](int x) { std::cout << x << ' '; } // printing lambda
);

std::cout << "│ ";

std::ranges::for_each(v, res1.fun); // uses negating lambda
std::ranges::for_each(v, res2.fun); // uses printing lambda
std::cout << '\n';
}

Output:¶

-1 -2 -3 │ 1 2 3

See also¶

pair implements binary tuple, i.e. a pair of values
(class template)
tuple implements fixed size container, which holds elements of possibly different
(C++11) types
(class template)