std::swap(s...d_multiset)(3)

🌸 NAME 🌸

std::swap(std::unordered_multiset) — yeah bestie, that's literally the whole name, it's std::swap(std::unordered_multiset). No notes. 💅

(This is page 3 of the C++ Standard Library section, btw, iykyk.)

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✨ Synopsis ✨

Ok so first thing: this whole thing lives in the header <unordered_set> 🫶

Here's the first overload, and she's been around a minute — (since C++11) — and the version without the noexcept biz has been (until C++17), so keep that in mind:

template< class Key, class Hash, class KeyEqual, class Alloc >

void swap( std::unordered_multiset<Key, Hash, KeyEqual, Alloc>& lhs,
           std::unordered_multiset<Key, Hash, KeyEqual, Alloc>& rhs
);

And then (since C++17) we got the glow-up version that tells you about exceptions up front:

template< class Key, class Hash, class KeyEqual, class Alloc >

void swap( std::unordered_multiset<Key, Hash, KeyEqual, Alloc>& lhs,
           std::unordered_multiset<Key, Hash, KeyEqual, Alloc>& rhs )

                     noexcept(/* see below */);

So what's the tea? This specializes the std::swap algorithm for std::unordered_multiset 💖 It swaps the contents of lhs and rhs, and under the hood it just calls lhs.swap(rhs). That's it. That's the whole vibe. ✨

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🎀 Parameters 🎀

• lhs, rhs — the containers whose contents we're swapping. The two besties exchanging fits. 👯‍♀️

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💖 Return value 💖

(none) — she gives you nothing back, because the swapping was the gift. 😌

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🔥 Complexity 🔥

Constant. Not me being obsessed with how fast that is. ⚡

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😭 Exceptions 😭

The noexcept specification, (since C++17):

noexcept(noexcept(lhs.swap(rhs)))

That's it, that's the whole clause, fr fr. 🫶

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🦋 Example 🦋

Run this code 🏃‍♀️

#include <algorithm>
#include <iostream>
#include <unordered_set>

int main()
{
    std::unordered_multiset<int> alice{1, 2, 3};
    std::unordered_multiset<int> bob{7, 8, 9, 10};

    auto print = [](const int& n) { std::cout << ' ' << n; };

    // Print state before swap
    std::cout << "Alice:";
    std::for_each(alice.begin(), alice.end(), print);
    std::cout << "\n" "Bob  :";
    std::for_each(bob.begin(), bob.end(), print);
    std::cout << '\n';

    std::cout << "-- SWAP\n";
    std::swap(alice, bob);

    // Print state after swap
    std::cout << "Alice:";
    std::for_each(alice.begin(), alice.end(), print);
    std::cout << "\n" "Bob  :";
    std::for_each(bob.begin(), bob.end(), print);
    std::cout << '\n';
}

Like, Alice and Bob are literally trading whole entire containers, iconic behavior honestly. 👑

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🌈 Possible output 🌈

Alice: 1 2 3
Bob  : 7 8 9 10
-- SWAP
Alice: 7 8 9 10
Bob  : 1 2 3

Not them fully switching lives 😭💀

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👑 See also 👑

• swap — swaps the contents (public member function)

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⭐ Category ⭐

• conditionally noexcept

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and that's the whole page, bestie, you ate that 🍓

Sign-off time 🎀 This little masterpiece lives over at http://cppreference.com, dated 2024.06.10 — go say hi, mwah 💜🧚