There are several main methods to implement polymorphism in C++:

• Virtual Functions:
  *Virtual function* is the primary way to implement polymorphism in C++. By declaring functions in the base class as *virtual* and overriding these *virtual* functions in derived classes, polymorphism can be achieved. When a function is called through a base class pointer or reference, the corresponding function version will be called based on the actual type of the object.

• Abstract Classes:
  An *abstract class* is a class that cannot be instantiated and contains at least one *pure virtual function* (a virtual function without implementation). Through abstract classes, derived classes can be forced to implement certain functions, thereby achieving polymorphism.

• Operator Overloading:
  C++ allows overloading of most operators, including arithmetic operators, relational operators, etc. Through operator overloading, polymorphism can be achieved, allowing different object types to use the same operators.

• Templates:
  Template is a mechanism that supports generic programming, and polymorphism can be achieved through template parameters. Templates allow writing code that is independent of data types, thus implementing polymorphism.

• Function Overloading:
  Function overloading refers to defining multiple functions with the same name within the same scope, as long as their parameter lists are different. Although function overloading itself is not a polymorphism implementation method, it can be combined with operator overloading to achieve polymorphism.

In conclusion, the main methods of implementing polymorphism in C++ include *virtual functions*, *abstract classes*, *operator overloading*, *templates*, and *function overloading*. Among these, *virtual functions* are the most commonly used and core method of implementing polymorphism.

In C++, polymorphism is a core feature that allows objects to appear in multiple forms, thereby enabling code reuse and scalability. Here are several ways polymorphism can achieve better code reuse:

• Base class interface definition: By defining a base class with virtual functions, we can provide a unified interface for all derived classes. This allows us to implement common functionality in the base class while leaving specific implementations to derived classes.

• Derived class implementation: Derived classes can override base class virtual functions to provide specific implementations. This way, we can implement the same interface in different derived classes with different behaviors, thus achieving code reuse.

• Dynamic binding: C++ allows decisions about which class’s functions to call to be made at runtime, known as dynamic binding or late binding. This means we can write code to manipulate base class pointers or references, and at runtime, the appropriate function is called based on the object’s actual type.

• Code extensibility: Since the code is written based on the base class interface, adding new derived classes won’t affect existing code. New derived classes only need to follow the base class interface, allowing program extension without modifying existing code.

• Reducing code duplication: Through polymorphism, we can reduce duplicate code. For example, if we have a function that needs to handle different types of objects, we can design it to accept base class type parameters and call virtual functions within the function, eliminating the need to write a version of the function for each type.

• Improving code maintainability: Since polymorphism allows us to separate common and specific code, when we need to modify common code, we don’t need to make changes in multiple places - just once in the base class.

In summary, polymorphism in C++ enables code reuse between different classes while maintaining flexibility and extensibility through a unified interface and dynamic binding mechanism. This allows us to write more generic and maintainable code while making it easy to add new features or modify existing ones.