std::experi...::multimap)(3)

✨ std::experimental::erase_if(std::multimap) ✨

okay bestie, quick vibe check: this is a page from the C++ Standard Libary manual (yes, that's how it's spelled up top, we don't fix, we don't judge 💅). It's the 3 section page for std::experimental::erase_if(std::multimap) and honestly? it's giving "tiny utility, huge slay." 🦋

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🎀 NAME 🎀

std::experimental::erase_if(std::multimap) — literally the same thing twice, because that's the name, and the name is iconic. periodt. ✨

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🌸 Synopsis 🌸

okay so the whole thing lives in the header <experimental/map>. write that down. 📝

template< class Key, class T, class Compare, class Alloc, class Pred >
void erase_if( std::multimap<Key, T, Compare, Alloc>& c, Pred pred );

and like, this is tagged (library fundamentals TS v2) — that's the version tea ☕ so don't come for me if you're on something else.

🫶 what it actually does

It erases all the elements that satisfy the predicate pred from the container. every single one. no crumbs left. 😭

It's equivalent to this little loop right here:

for (auto i = c.begin(), last = c.end(); i != last;)
{
    if (pred(*i))
        i = c.erase(i);
    else
        ++i;
}

like, that's literally it. that's the whole personality. main character energy in four lines. 👑

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💖 Parameters 💖

• c — the container you're erasing from, aka the victim 🫶
• pred — the predicate that decides which elements get erased. it's the judge, jury, and vibe checker. ⭐

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⚡ Complexity ⚡

Linear. that's it. that's the whole section. lowkey the shortest paragraph on the page and honestly? respect. 🌈

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🔥 Example 🔥

the code is right here, run it, don't run it, idk, live your truth:

// Run this code

#include <experimental/map>
#include <iostream>

template<typename Os, typename Container>
inline Os& operator<<(Os& os, Container const& cont)
{
    os << '{';
    for (const auto& item : cont)
        os << '{' << item.first << ", " << item.second << '}';
    return os << '}';
}

int main()
{
    std::multimap<int, char> data{{1, 'a'},{2, 'b'},{3, 'c'},{4, 'd'},
                                  {5, 'e'},{4, 'f'},{5, 'g'},{5, 'g'}};
    std::cout << "Original:\n" << data << '\n';
    std::experimental::erase_if(data, [](const auto& item)
    {
        return (item.first & 1) == 1;
    });
    std::cout << "Erase items with odd keys:\n" << data << '\n';
}

🍓 Output 🍓

Original:
{{1, a}{2, b}{3, c}{4, d}{4, f}{5, e}{5, g}{5, g}}
Erase items with odd keys:
{{2, b}{4, d}{4, f}}

not the odd keys getting absolutely obliterated 😭 they really said "not you" and meant it 💀

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👀 See also 👀

• remove — removes elements satisfying specific criteria
• remove_if (function template) — bestie cousin of the above, also a function template

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🧚 Category 🧚

• Noindexed pages

(that's the category, ngl it's giving "left on read" but we keep it, we don't erase it — see what I did there 🙈)

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heads up bestie: this page is tagged with (library fundamentals TS v2), so it's a TS thing, a technical specification, not the fully merged mainline standard. read the tag, know the tag, love the tag. 💜

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okay that's the whole page!! 💖✨🎀🦋🌸💅🫶

cute little sign-off for you: this came from http://cppreference.com, dated 2024.06.10, and it's the std::experi...::multimap)(3) page — yes the title is truncated with dots in the header, slay, we reproduce it faithfully, no cap. byeee 👑⭐