namespace {
 
template<typename T>
class Foo {
public:
	Foo(T value)
	{
		std::cout << "Created Foo, type id: " << typeid(T).name() << ", value: " << value << "\n";
	}
};
 
template<typename T>
class Foo2 {
public:
	Foo2(T value)
	{
		std::cout << "Created Foo2, type id: " << typeid(T).name() << ", value: " << value << "\n";
	}
};
 
// User-defined deduction guide 
template<typename T> Foo2(T)->Foo2<T>;
 
template<typename T> using MyAlias = T;
 
template<typename T>
class Foo3 {
public:
	Foo3(const std::initializer_list<T>& list) : vec_(list) {}
	void print() const
	{
		for (const auto& val : vec_) {
			std::cout << val << " ";
		}
		std::cout << "\n";
	}
 
private:
	std::vector<T> vec_;
};
 
} // namespace
 
int test_ctad()
{
	// 只要能根據(jù)初始值推導(dǎo)出所有模板參數(shù)就可以使用類(lèi)模板參數(shù)推導(dǎo)
	// 推導(dǎo)過(guò)程支持所有方式的初始化(只要保證初始化是有效的)
	std::pair p(2, 4.5);     // deduces to std::pair<int, double> p(2, 4.5);
	std::tuple t(4, 3, 2.5); // same as auto t = std::make_tuple(4, 3, 2.5);
	std::complex c{ 5.1, 3.3 }; // std::complex<double>
	std::mutex mx;
	std::lock_guard lg{ mx }; // std::lock_guard<std::mutex>
	std::vector vec{ "hello", "world" }; // std::vector<const char*>
 
	std::vector v1{ 42 };
	std::vector v2{ v1 }; // v2也是一個(gè)std::vector<int>,這是花括號(hào)初始化總是把列表中的參數(shù)作為元素這一規(guī)則的一個(gè)例外
	// 然而,如果用多于一個(gè)元素的初值列來(lái)初始化的話,就會(huì)把傳入的參數(shù)作為元素并推導(dǎo)出其類(lèi)型作為模板參數(shù)
	std::vector vv{ v1, v2 }; // vv是一個(gè)vector<vector<int>>
 
 
	// 1.Class Template Argument Deduction(CTAD)
	// not specifying the type of the template
	auto foo11 = Foo(88); // Created Foo, type id: int, value: 88
	auto foo12 = Foo("Beijing"); // Created Foo, type id: char const * __ptr64, value: Beijing
 
	// specifying the type of the template
	Foo<int> foo21(88); // Created Foo, type id: int, value: 88
	Foo<const char*> foo22("Beijing"); // Created Foo, type id: char const * __ptr64, value: Beijing
 
 
	// 2.User-defined deduction guides
	// not specifying the type of the template
	auto foo31 = Foo2(88); // Created Foo2, type id: int, value: 88
	auto foo32 = Foo2("Beijing"); // Created Foo2, type id: char const * __ptr64, value: Beijing
 
 
	// 3.the deduction for alias templates
	MyAlias<int> alias1{ 88 };
	MyAlias<std::string> alias2{ "Beijing" };
 
	std::cout << "alias1: " << alias1 << "\n"; // alias1: 88
	std::cout << "alias2: " << alias2 << "\n"; // alias2: Beijing
 
	// reference: https://www.geeksforgeeks.org/class-template-argument-deduction-in-cpp-17/
	auto foo41 = Foo3({ 1, 2, 3, 4, 5 });
	foo41.print(); // 1 2 3 4 5
 
	return 0;
}