C++ lambda 表达式的生命周期是多少?

I understand that C++ lambda syntax is just sugar for making an instance of an anonymous class with a call operator and some state, and I understand the lifetime requirements of that state (decided by whether you capture by value of by reference.) But what is the lifetime of the lambda object itself? In the following example, is the std::function instance returned going to be useful?

std::function<int(int)> meta_add(int x) {
    auto add = [x](int y) { return x + y; };
    return add;
}

如果是，它是如何工作的?这对我来说似乎有点太神奇了 - 我只能想象它通过 std::function 复制我的整个实例来工作，这取决于我捕获的内容可能非常繁重 - 过去我已经std::function 主要用于裸函数指针，复制它们很快.鉴于 std::function 的类型擦除，它似乎也有问题.

struct lambda {
   lambda(int x) : x(x) { }
   int operator ()(int y) { return x + y; }

private:
   int x;
};

std::function<int(int)> meta_add(int x) {
   lambda add(x);
   return add;
}