struct Point
{
	int _x;
	int _y;
};
class Date
{
public:
	Date(int year, int month, int day)
		:_year(year)
		, _month(month)
		, _day(day)
	{
		cout << "Date(int year, int month, int day)" << endl;
	}
private:
	int _year;
	int _month;
	int _day;
};
int main()
{
	int x1 = 1;
	int x2{ 2 };
	int array1[]{ 1, 2, 3, 4, 5 };
	int array2[5]{ 0 };
	Point p{ 1, 2 };

	// C++11中列表初始化也可以适用于new表达式中
	int* pa = new int[4] { 0 };

	//C++98
	Date d1(2022, 1, 1);
	//C++11
	Date d2{ 2022, 1, 2 };
	Date d3 = { 2022, 1, 3 };
	return 0;
}

1.2 std::initializer_list

int main()
{
	vector<int> v = { 1,2,3,4 };
	list<int> lt = { 1,2 };
	// 这里{"sort", "排序"}会先初始化构造一个pair对象
	map<string, string> dict = { {"sort", "排序"}, {"insert", "插入"} };
	// 使用大括号对容器赋值
	v = { 10, 20, 30 };
	return 0;
}

	//先构造再拷贝 -> 编译器优化 -> 直接构造
	vector<int> v1 = { 1,2,3,4,5,6,7,8,9 };
	//直接构造
	vector<int> v2{ 1,2,3,4,5,6,7,8,9 };

2. 声明

2.1 auto

template<class T1, class T2>
void F(T1 t1, T2 t2)
{
	decltype(t1 * t2) ret;
	cout << typeid(ret).name() << endl;
}
int main()
{
	const int x = 1;
	double y = 2.2;
	decltype(x * y) ret; // ret的类型是double
	decltype(&x) p;      // p的类型是int*
	cout << typeid(ret).name() << endl;
	cout << typeid(p).name() << endl;
	F(1, 'a');
	return 0;
}

int main() {
	int array[] = { 1, 2, 3, 4, 5 };
	// 如果要进行修改，就必须要引用
	for (auto& e : array)
		e *= 2;
	// 如果只是访问，可以不用引用
	for (auto e : array)
		cout << e << " " << endl;
	return 0;
}

3.2 范围for的使用条件

int main() {
	vector<int> v = { 1, 2, 3, 4, 5 };
	vector<int>::iterator it = v.begin();

	for (auto e : v)
		cout << e << " ";

	cout << endl;

	for (; it != v.end(); it++)
		cout << *it << " ";

	return 0;
}

5.4 禁止生成默认函数的关键字delete

void Test()
{
	auto f = [] {cout << "hello world" << endl; };
	f();
}

class Date
{
public:
	Date(int year = 1, int month = 1, int day = 1)
		:_year(year)
		, _month(month)
		, _day(day)
	{
		cout << "Date(int year, int month, int day)" << endl;
	}

	Date(const Date& d)
		:_year(d._year)
		, _month(d._month)
		, _day(d._day)
	{
		cout << "Date(const Date& d)" << endl;
	}
private:
	int _year = 1;
	int _month = 1;
	int _day = 1;
};

int main()
{
	auto DateLess = [](const Date* p1, const Date* p2)
	{
		return p1 < p2;//偷懒直接比指针
	};
	cout << typeid(DateLess).name() << endl;

	// lambda对象支持拷贝构造
	auto copy(DateLess);

	// lambda对象禁掉默认构造
	// decltype(DateLess) xx;//运行报错

    //为了下面的代码运行通过，还得有比较对象DateLess，因为lambda对象不会默认构造
	priority_queue<Date*, vector<Date*>, decltype(DateLess)> p1(DateLess);

	return 0;
}

class Rate
{
public:
	Rate(double rate) : _rate(rate)
	{}

	double operator()(double money, int year)
	{
		return money * _rate * year;
	}
private:
	double _rate;
};

int main()
{
	double rate = 0.49;
	Rate r1(rate);
	r1(10000, 2);

	auto r2 = [=](double monty, int year)->double {return monty * rate * year;};
	r2(10000, 2);

	auto f1 = [] {cout << "hello world" << endl; };
	auto f2 = [] {cout << "hello world" << endl; };

	f1();
	f2();

	return 0;
}

8. 包装器

8.1 function包装器

//std::function在头文件<functional>
// 类模板原型如下
template <class T> function;     // undefined
template <class Ret, class... Args>
class function<Ret(Args...)>;

模板参数说明：
Ret : 被调用函数的返回类型
Args…：被调用函数的形参

        function包装器也叫作适配器。C++中的function本质是一个类模板，也是一个包装器，是对可调用对象的再封装，统一类型，可调用对象有函数指针/函数名、仿函数、lambda表达式等。   
         对于编译器而言，下面的代码模useF板会实例化3份：

template<class F, class T>
T useF(F f, T x)
{
	static int count = 0;
	cout << "count:" << ++count << endl;
	cout << "count:" << &count << endl;

	return f(x);
}

double f(double i)
{
	return i / 2;
}

struct Functor
{
	double operator()(double d)
	{
		return d / 3;
	}
};

int main()
{
	// 函数名
	cout << useF(f, 11.11) << endl;

	// 函数对象
	cout << useF(Functor(), 11.11) << endl;

	// lamber表达式
	cout << useF([](double d)->double { return d / 4; }, 11.11) << endl;

	return 0;
}

int main()
{
	// 调整参数的个数
	// 某些参数绑死
	function<double(double, double)> fc4 = bind(&Plus::plusd, Plus(), placeholders::_1, placeholders::_2);
	cout << fc4(2, 3) << endl;

	function<double(double)> fc5 = bind(&Plus::plusd, Plus(), placeholders::_1, 20);
	cout << fc5(2) << endl;

	return 0;
}