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std::ranges::in_fun_result

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< cpp‎ | algorithm‎ | ranges
 
C++
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Permutations
Numeric operations
(C++23)
Fold operations
Operations on uninitialized storage
Return types
 
Return types of constrained algorithms
Return types
in_fun_result
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++23)
(C++23)
 
Defined in header <algorithm>
template< class I, class F >
struct in_fun_result;
 (since C++20)

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.

Contents

[edit] 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.

[edit] Data members

std::ranges::in_fun_result::in

[[no_unique_address]] I in;

a value (that is supposed to be an iterator)

std::ranges::in_fun_result::fun

[[no_unique_address]] F fun;

a value (that is supposed to be a function object)

[edit] 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>

constexpr operator in_fun_result<I2, F2>() const &;
 (1)
template<class I2, class F2>

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

constexpr operator in_fun_result<I2, F2>() &&;
 (2)

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)};.

[edit] Standard library

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

Algorithm functions
(C++20)
 applies a function to a range of elements
(niebloid) [edit]
(C++20)
 applies a function object to the first n elements of a sequence
(niebloid) [edit]

[edit] 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)};
        }
    };
}

[edit] 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.

[edit] Example

Run this code
#include <algorithm>
#include <iostream>
#include <iterator>
#include <ranges>
 
int main()
{
    int v[] {1, 2, 3};
 
    const auto [last, negate] = std::ranges::for_each_n(v, std::size(v),
        [](int& x) { return x = -x; });
 
    const auto result = std::ranges::for_each(std::cbegin(v), last,
        [](int x) { std::cout << x << ' '; });
    std::cout << "│ ";
 
    std::ranges::for_each(v, negate);
    std::ranges::for_each(v, result.fun);
    std::cout << '\n';
}

Output: 

-1 -2 -3 │ 1 2 3

[edit] See also

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