TEST.ixx

#define _CRT_SECURE_NO_WARNINGS

#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()"); }
};

template <typename F, typename... Args>
class scope_guard {
public:
	scope_guard(F&& f, Args&&... args) : f_(std::forward<F>(f)), args_(std::forward<Args>(args)...) {}
	~scope_guard() {
		std::apply(f_, args_);
	}
private:
    F f_;
	std::tuple<Args...> args_;
};

template <typename F, typename... Args>
scope_guard(F&& f, Args&&... args) -> scope_guard<F, Args...>;

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);
    }
}