std::ranges::in_fun_result

 

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Symbols index

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Constrained algorithms

All names in this menu belong to namespace std::ranges

Non-modifying sequence operations

all_ofany_ofnone_of for_each for_each_n    countcount_if adjacent_find mismatch equal lexicographical_compare    containscontains_subrange (C++23)(C++23) findfind_iffind_if_not find_lastfind_last_iffind_last_if_not (C++23)(C++23)(C++23)   find_end find_first_of search search_n starts_with (C++23) ends_with (C++23)

Modifying sequence operations

copycopy_if copy_n copy_backward    move move_backward shift_leftshift_right (C++23)(C++23)   fill fill_n generate generate_n    transform swap_ranges    shuffle sample removeremove_if replacereplace_if reverse rotate remove_copyremove_copy_if    unique replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy

Partitioning operations

is_partitioned    partition_point    partition    partition_copy    stable_partition

Sorting operations

is_sorted is_sorted_until     sort stable_sort         partial_sort       nth_element partial_sort_copy

Binary search operations (on sorted ranges)

lower_bound         upper_bound         binary_search      equal_range

Set operations (on sorted ranges)

merge inplace_merge       set_difference set_intersection    set_union          includes set_symmetric_difference

Heap operations

is_heap is_heap_until       make_heap           sort_heap push_heap pop_heap

Minimum/maximum operations

max max_element         min min_element         minmax minmax_element     clamp

Permutation operations

is_permutation      next_permutation    prev_permutation

Fold operations

fold_left (C++23) fold_left_first (C++23)   fold_right (C++23) fold_right_last (C++23)   fold_left_with_iter (C++23) fold_left_first_with_iter (C++23)

Numeric operations iota (C++23)             Random number generation generate_random (C++26)

Operations on uninitialized storage

construct_at    destroy destroy_n destroy_at uninitialized_copy    uninitialized_move uninitialized_fill uninitialized_copy_n    uninitialized_move_n uninitialized_fill_n uninitialized_default_construct uninitialized_default_construct_n uninitialized_value_construct uninitialized_value_construct_n

Return types

in_fun_result in_in_result in_found_result    in_out_result in_in_out_result    in_out_out_result    min_max_result out_value_result (C++23) in_value_result (C++23)

 

Return types of constrained algorithms

Return types

ranges::in_found_result

ranges::in_fun_result

ranges::in_in_out_result

ranges::in_in_result

ranges::in_out_out_result

ranges::in_out_result

ranges::in_value_result (C++23)

ranges::min_max_result

ranges::out_value_result (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.

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> 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)};.

Standard library

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

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

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 (C++11)	implements fixed size container, which holds elements of possibly different types (class template)