CODEWITHSUNDEEP
c++c++20
Andrew Tomazos
Andrew Tomazos

Reputation: 68648

Read/write all values of a std::multimap with a given key in C++20?

Suppose I have some function:

void mutate(V& v);

that reads/writes v - and I want to write a function:

void mutate_map_values(std::multimap<K,V>& m, K k);

that applies mutate to all values of m that have key k.

What's the most succinct way to implement mutate_map_values in C++20?

Upvotes: 2

Views: 236

Answers (1)

StoryTeller - Unslander Monica
StoryTeller - Unslander Monica

Reputation: 170084

std::ranges::subrange is a utility class that's constructible from anything that is like a pair of iterators. Which fits with what std::multimap::equal_range already returns. Combining the two, we may write the desired function as follows in C++20:

#include <ranges>

void mutate_map_values(std::multimap<K,V>& m, K k) {
    using namespace std::ranges;
    for (auto& [_, v] : subrange(m.equal_range(k))) {
        mutate(v);
    }
}

Upvotes: 5

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