std::erase_...::flat_set)(3)

💖 std::erase_...::flat_set)(3) 💖

okay bestie, this page is straight out of the C++ Standard Libary manual (yes, that's literally how it's spelled there), and it's about std::erase_if(std::flat_set). it's giving very specific, very useful, very C++23 energy. let's get into it ✨

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🎀 NAME 🎀

std::erase_if(std::flat_set) — std::erase_if(std::flat_set)

✨ Synopsis ✨

Defined in header <flat_set>

template< class Key, class Compare, class KeyContainer,

          class Pred >
std::flat_set<Key, Compare, KeyContainer>::size_type         (since
C++23)
    erase_if( std::flat_set<Key, Compare, KeyContainer>& c,

              Pred pred );

Erases all elements that satisfy the predicate pred from c.

The predicate pred is satisfied if the expression bool(pred(std::as_const(e))) is true, where e is some element in c.

🚨 real talk: Key must be MoveAssignable. Otherwise, the behavior is undefined. no cap, that part matters.

💅 Parameters 💅

• c — container adaptor from which to erase
• pred — predicate that returns true if the element should be erased

🫶 Return value 🫶

The number of erased elements. that's it, that's the tea 💖

🔥 Complexity 🔥

Exactly c.size() applications of the predicate pred.

💀 Exceptions 💀

If erase_if throws, c remains in valid but unspecified (maybe empty) state. periodt.

🌸 Notes 🌸

The algorithm is stable, that is, the order of elements that are not deleted remains unchanged. slay for predictable vibes ✨

🐚 Example 🐚

// Run this code

#include <iostream>
#include <flat_set>

void println(auto rem, auto const& container)
{
    std::cout << rem << '{';
    for (char sep[]{0, ' ', 0}; const auto& item : container)
        std::cout << sep << item, *sep = ',';
    std::cout << "}\n";
}

int main()
{
    std::flat_set data{3, 3, 4, 5, 5, 6, 6, 7, 2, 1, 0};
    println("Original:\n", data);

    auto divisible_by_3 = [](auto const& x) { return (x % 3) == 0; };

    const auto count = std::erase_if(data, divisible_by_3);

    println("Erase all items divisible by 3:\n", data);
    std::cout << count << " items erased.\n";
}

Output:

Original:
{0, 1, 2, 3, 4, 5, 6, 7}
Erase all items divisible by 3:
{1, 2, 4, 5, 7}
3 items erased.

👀 See also 👀

• remove — removes elements satisfying specific criteria
• remove_if — (function template)

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okay bye bestie 💅 source: http://cppreference.com; version/date: 2024.06.10; manual page: std::erase_...::flat_set)(3) 🫶✨