当我将运算符作为模板重载时会发生什么？

Question

I am writing some notes, and just for the sake of compiling, I added an operator<< overloaded function for the ostream as a template . It compiles just fine but, since I overloaded the operator with class type inside the <> of template and passed that type as the second input for the overloaded function, won't it use the new operator for EVERY class that I define from now on? Here's my code for reference. It's purely for note purposes, it has no functionality.

template <class type>
ostream& operator<< (ostream& s, type x){
  s << x.getsmth();
  //...
}

Answer 1

I'm myself a novice when it comes to SFINAE, but it seems like you are correct, this template will be used for classes which don't offer getsmth() , even though the body doesn't compile. You can prevent this from happening with SFINAE though, this seems to work as expected:

template <class T, typename = decltype(T().getSomething())>
std::ostream& operator<< (std::ostream& s, T& x){
  s << x.getSomething();
  return s;
}

Demo: http://cpp.sh/8fyk