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Showing content from https://en.cppreference.com/w/cpp/algorithm/../symbol_index/../algorithm/ranges/replace.html below:

std::ranges::replace, std::ranges::replace_if - cppreference.com

Call signature

Replaces all elements satisfying specific criteria with new_value in the range [first, last).

Replaces all elements that are equal to

, using

to compare.

Replaces all elements for which the predicate

evaluates to

, where evaluating expression is

.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

An iterator equal to last.

Exactly ranges::distance(first, last) applications of the corresponding predicate comp and any projection proj.

Because the algorithm takes old_value and new_value by reference, it may have unexpected behavior if either is a reference to an element of the range [first, last).

struct replace_fn
{
    template<std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
             class T1 = std::projected_value_t<I, Proj>, class T2 = T1>
    requires std::indirectly_writable<I, const T2&> && 
             std::indirect_binary_predicate
                 <ranges::equal_to, std::projected<I, Proj>, const T1*>
    constexpr I operator()(I first, S last, const T1& old_value,
                           const T2& new_value, Proj proj = {}) const
    {
        for (; first != last; ++first)
            if (old_value == std::invoke(proj, *first))
                *first = new_value;
        return first;
    }
 
    template<ranges::input_range R, class Proj = std::identity
             class T1 = std::projected_value_t<ranges::iterator_t<R>, Proj>,
             class T2 = T1>
    requires std::indirectly_writable<ranges::iterator_t<R>, const T2&> &&
             std::indirect_binary_predicate<ranges::equal_to,
             std::projected<ranges::iterator_t<R>, Proj>, const T1*>
    constexpr ranges::borrowed_iterator_t<R>
        operator()(R&& r, const T1& old_value,
                   const T2& new_value, Proj proj = {}) const
    {
        return (*this)(ranges::begin(r), ranges::end(r), old_value,
                       new_value, std::move(proj));
    }
};
 
inline constexpr replace_fn replace{};

struct replace_if_fn
{
    template<std::input_iterator I, std::sentinel_for<I> S,
             class Proj = std::identity, class T = std::projected_value_t<I, Proj>,
             std::indirect_unary_predicate<std::projected<I, Proj>> Pred>
    requires std::indirectly_writable<I, const T&>
    constexpr I operator()(I first, S last, Pred pred,
                           const T& new_value, Proj proj = {}) const
    {
        for (; first != last; ++first)
            if (!!std::invoke(pred, std::invoke(proj, *first)))
                *first = new_value;
        return std::move(first);
    }
 
    template<ranges::input_range R, class Proj = std::identity,
             class T = std::projected_value_t<ranges::iterator_t<R>, Proj>
             std::indirect_unary_predicate
                 <std::projected<ranges::iterator_t<R>, Proj>> Pred>
    requires std::indirectly_writable<ranges::iterator_t<R>, const T&>
    constexpr ranges::borrowed_iterator_t<R>
        operator()(R&& r, Pred pred, const T& new_value, Proj proj = {}) const
    {
        return (*this)(ranges::begin(r), ranges::end(r), std::move(pred),
                       new_value, std::move(proj));
    }
};
 
inline constexpr replace_if_fn replace_if{};

#include <algorithm>
#include <array>
#include <complex>
#include <iostream>
 
void println(const auto& v)
{
    for (const auto& e : v)
        std::cout << e << ' ';
    std::cout << '\n';
}
 
int main()
{
    namespace ranges = std::ranges;
 
    std::array p{1, 6, 1, 6, 1, 6};
    println(p);
    ranges::replace(p, 6, 9);
    println(p);
 
    std::array q{1, 2, 3, 6, 7, 8, 4, 5};
    println(q);
    ranges::replace_if(q, [](int x) { return 5 < x; }, 5);
    println(q);
 
    std::array<std::complex<double>, 2> nums{{{1, 3}, {1, 3}}};
    println(nums);
    #ifdef __cpp_lib_algorithm_default_value_type
        ranges::replace(nums, {1, 3}, {4, 2});
    #else
        ranges::replace(nums, std::complex<double>{1, 3}, std::complex<double>{4, 2});
    #endif
    println(nums);
}

Output:

1 6 1 6 1 6
1 9 1 9 1 9
1 2 3 6 7 8 4 5
1 2 3 5 5 5 4 5
(1,3) (1,3)
(4,2) (4,2)

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