C++: initializer_list

总结自：

• std::initializer_list
• Variable number of arguments in C++?

---

首先它是一个 template，然后它是在 std 空间下，头文件是 #include <initializer_list>，但是在用的时候好像并不需要写这句 #include。

Objects of initializer_list are automatically constructed by the compiler from initialization list declarations, which is a list of comma-separated elements enclosed in braces:

auto il = { 10, 20, 30 };  // il is an initializer_list 

for (auto i : { 1, 2, 3, 4, 5 })
	std::cout << i << "\n";

Constructors taking only one argument of initializer_list are a special kind of constructor, called initializer-list constructor. 它的语法有点奇怪，我们称为 list initialization：

struct myclass {
	myclass(int,int) { ... }
	myclass(initializer_list<int>) { ... }
};

myclass foo{10,20};  // calls initializer_list constructor
myclass bar(10,20);  // calls (int,int) constructor 

然后你会发现 initializer_list 其实是个挺好的 variable argument list（可变参数列表）的 solution，比 func(...) 简单多了：

template <class T>
void func(std::initializer_list<T> list) {
    for(T elem : list) {
        std::cout << elem << std::endl;
    }
}

int main() {
	func({10, 20, 30, 40});
	func({"Hello", "World"});
}