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int main(){
    std::cout << "乐 :{} *\n"_f(5);
    std::cout << "乐 :{0} {0} *\n"_f(5);
    std::cout << "乐 :{:b} *\n"_f(0b01010101);
    std::cout << "{:*<10}"_f("卢瑟");
    std::cout << '\n';
    int n{};
    std::cin >> n;
    std::cout << "π：{:.{}f}\n"_f(std::numbers::pi_v<double>, n);
}

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#include<iostream>
class ComponentBase{
protected:
    static inline std::size_t component_type_count = 0;
};
template<typename T>
class Component : public ComponentBase{
public:
    // todo...
    // Change the current template class in any way so that for any type X, if it inherits from Component

    // Then X::component type id() will get a unique id of type size t (different values should be returned for different X types)值应不同）
    // Requirements: std::type info cannot be used (the typeid keyword is disabled), and all ids are consecutive starting from 0
};
class A : public Component<A>
{};
class B : public Component<B>
{};
class C : public Component<C>
{};
int main()
{
    std::cout << A::component_type_id() << std::endl;
    std::cout << B::component_type_id() << std::endl;
    std::cout << B::component_type_id() << std::endl;
    std::cout << A::component_type_id() << std::endl;
    std::cout << A::component_type_id() << std::endl;
    std::cout << C::component_type_id() << std::endl;
}

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#include <cstdio>
#include <cassert>

#include <stdexcept>
#include <iostream>
#include <functional>

struct X {
    X() { puts("X()"); }
    X(const X&) { puts("X(const X&)"); }
    X(X&&) noexcept { puts("X(X&&)"); }
    ~X() { puts("~X()"); }
};

int main() {
    {
        // scope_guard的作用之一，是让各种C风格指针接口作为局部变量时也能得到RAII支持
        // 这也是本题的基础要求
        FILE * fp = nullptr;
        try{
            fp = fopen("test.txt","a");
            auto guard = scope_guard([&] {
                fclose(fp);
                fp = nullptr;
            });

            throw std::runtime_error{"Test"};
        } catch(std::exception & e){
            puts(e.what());
        }
        assert(fp == nullptr);
    }
    puts("----------");
    {
        // 附加要求1，支持函数对象调用
        struct Test {
            void operator()(X* x) {
                delete x;
            }
        } t;
        auto x = new X{};
        auto guard = scope_guard(t, x);
    }
    puts("----------");
    {
        // 附加要求2，支持成员函数和std::ref
        auto x = new X{};
        {
            struct Test {
                void f(X*& px) {
                    delete px;
                    px = nullptr;
                }
            } t;
            auto guard = scope_guard{&Test::f, &t, std::ref(x)};
        }
        assert(x == nullptr);
    }
}

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int main()
{
    std::vector v{1, 2, 3};
    std::function f {[](const int& i) {std::cout << i << ' '; } };
    auto f2 = [](int& i) {i *= i; };
    v | f2 | f;
}