c++ - Is there any difference if we define friend function inside or outside of class

Question

What is the difference between defining friend function inside the class or declaring inside and define outside of the class. Also why it is possible to place definition inside the class, as friend function are not member of the class.

Answer 1

Friend functions defined inside the class can only be looked up through ADL when called from outside the class. Functions defined outside of the class can be found even without ADL.