• this
    It’s a pointer
    You can use keyword “this” to refer to this instance inside a class definition.
    One of the main usage of keyword this is to resolve ambiguity between the names of data member and function parameter. For example,
class Circle {
   double radius;                 // Member variable called "radius"
   void setRadius(double radius) { // Function's argument also called "radius"
      this->radius = radius;
         // "this.radius" refers to this instance's member variable
         // "radius" resolved to the function's argument.

Return the reference of the object (return this), 套娃