C++ how does lambda to std::function conversion implemented?

In the following code:

struct Data{
   int i;
   Data(int i) : i(i){}
};
void test_data(Data){}

void test(std::function<void()>){}

int main(){
   test([](){});     // how does it possible?
   test({ [](){} }); // there is no need for extra {}

   test_data(1);       // But this one not work!
   test_data({1});     // This one ok.
}

How does it possible that I can simply pass lambda to a function, that accepts std::function and it will be fine, while I can't do the same with my custom Data?

P.S. As I understand there is some conversion operator from lambda to std::function. But lambda is compiler construction, and std::function is a library construct. And I see nothing special here in it http://ift.tt/2nYlDnF