子魂.cpp

#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()"); }
};

class scope_guard
{
public:
    template<typename FuncType, typename... Args>
    scope_guard(FuncType&& func, Args&&... args)
    {
        lambda_ = [&func, &args...](){
            std::invoke(std::forward<decltype(func)>(func), std::forward<decltype(args)>(args)...);
        };
    }
    scope_guard(const scope_guard&) = delete;
    ~scope_guard()
    {
        lambda_();
    }

    scope_guard& operator=(const scope_guard&) = delete;

private:
    std::function<void(void)> lambda_;
};

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);
    }
}