std::flat_m...insert_range(3)

💖 NAME 💖

okay so bestie, welcome to <pink>std::flat_m...insert_range(3)</pink> from the <pink>C++ Standard Libary</pink> manual — aka the std::flat_map::insert_range page. And yes, the NAME line is literally std::flat_map::insert_range — std::flat_map::insert_range twice, because repetition is iconic. 🦋

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✨ Synopsis ✨

Here’s the signature, no cap:

template< container-compatible-range<value_type> R >  (since C++23)
void insert_range( R&& rg );

It inserts a copy of each element in the range rg into underlying containers c as if by:

for (const auto& e : rg)
{
    c.keys.insert(c.keys.end(), e.first);
    c.values.insert(c.values.end(), e.second);
}

Then, it sorts the range of newly inserted elements with respect to value_comp(). It merges the resulting sorted range and the sorted range of pre-existing elements into a single sorted range. Finally, it erases the duplicate elements as if by:

auto zv = views::zip(c.keys, c.values);
auto it = ranges::unique(zv, key_equiv(compare)).begin();
auto dist = std::distance(zv.begin(), it);
c.keys.erase(c.keys.begin() + dist, c.keys.end());
c.values.erase(c.values.begin() + dist, c.values.end());

Each iterator in the range rg is dereferenced exactly once. The behavior is undefined if rg overlaps with the container.

🚨 undefined behavior alert: if rg overlaps with the container, that’s undefined behavior — do not do that, bestie.

Information on iterator invalidation is copied from here 👀

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🫶 Parameters 🫶

• rg — a container compatible range, that is, an input_range whose elements are convertible to T.

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🌈 Return value 🌈

(none) — that’s it, the void is voiding. 💀

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🔥 Complexity 🔥

N + M·log(M), where N is size() before the operation and M is ranges::distance(rg).

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🎀 Notes 🎀

Since insert_range performs an in-place merge operation, that may allocate memory. Lowkey important: it may allocate memory. 🫶

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🧚 Example 🧚

// Run this code

#include <iostream>
#include <flat_map>
#include <utility>

void println(auto, auto const& container)
{
    for (const auto& [key, value] : container)
        std::cout << '{' << key << ',' << value << '}' << ' ';
    std::cout << '\n';
}

int main()
{
    auto container = std::flat_map{std::pair{1, 11}, {3, 33}, {2, 22},
       {4, 44}};
    const auto rg = {std::pair{-1, -11}, {3, -33}, {-2, -22}};
#ifdef __cpp_lib_containers_ranges
    container.insert_range(rg);
#else
    container.insert(rg.begin(), rg.end());
#endif
    println("{}", container);
}

Output:

{-2,-22} {-1,-11} {1,11} {2,22} {3,33} {4,44}

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👑 See also 👑

• insert — inserts elements (public member function)

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source/version: http://cppreference.com · date: 2024.06.10 · page: std::flat_m...insert_range(3). bye bestie, go insert those ranges and slay 💅✨👑