constexpr auto make_checker() {
    return [](int x) consteval {
        return x % 3 == 0 || x % 5 == 0;
    };
}

int main() {
    auto checker = make_checker();
    std::vector<int> numbers{1, 3, 5, 9, 10, 14, 15};
    auto filtered = numbers | std::views::filter([&](int x) {
        return checker(x);
    });
    for (int x : filtered)
        std::print("{} ", x);
}

#include <iostream>
using namespace std;

class Base {
public:
    Base() {
        cout << "Base constructor: ";
        call();
    }
    virtual void call() { cout << "Base::call\n"; }
};

class Derived : public Base {
    int x = init();

    int init() {
        cout << "Derived::init\n";
        return 42;
    }

public:
    Derived() {
        cout << "Derived constructor\n";
    }

    void call() override {
        cout << "Derived::call, x = " << x << "\n";
    }
};

int main() {
    Derived d;
    return 0;
}

Derived::init
Derived constructor

Derived::init
Derived constructor

Base constructor: Derived::call, x = 42
Derived constructor

Derived::call, x = <undefined>
Derived::init
Derived constructor

#include <iostream>
#include <vector>

struct Foo {
    Foo() { std::cout << "Ctor\n"; }
    ~Foo() { std::cout << "Dtor\n"; }
    Foo(const Foo&) { std::cout << "Copy\n"; }
    Foo(Foo&&) noexcept { std::cout << "Move\n"; }
};

int main() {
    std::vector<Foo> v;
    v.reserve(3);  // Резервируем место под 3 элемента

    std::cout << "--- Pushing ---\n";
    for (int i = 0; i < 3; ++i) {
        v.push_back(Foo());
    }

    std::cout << "--- Done ---\n";
}

--- Pushing ---
Ctor
Move
Dtor
Ctor
Move
Dtor
Ctor
Move
Dtor
--- Done ---
Dtor
Dtor
Dtor

// Резервирует память, не создаёт объекты
v.reserve(10);

// Создаёт 10 объектов Foo
v.resize(10);

v.emplace_back();  // Вызывает конструктор Foo напрямую внутри вектора