Declare Method
Method and Function can be the same name
Method and Field can not have the same name
Can declare another method name in the same file for different type
To modify instance value directly, use pointer to declare Method
Pointer type can't be declared as method receiver.
When a receiver is declared as a pointer, client code should use & to call method.
But Go will convert it implicitly
Can not call method in *Point because no address if temp value. Ex. Point{}.add(2)//compile error
Ways to declare and use receiver
