Class templates: template arguments, template specialization, template inheritance in C++

In C++, a class template is a class that can be parameterized with one or more types. The template allows you to define a generic class that can be used with different types without having to write a separate class for each type.

To define a class template in C++, we use the following syntax:

template 
class MyClass {
public:
    T getData() { return data; }
    void setData(T value) { data = value; }

private:
    T data;
};

Here, `MyClass` is the name of the class, and `T` is the template parameter. The template parameter can be any valid C++ type, such as `int`, `float`, or a user-defined class. The class members can use the template parameter as if it were a regular variable of that type.

To instantiate a class template, you must specify the template argument, which is the specific type that the template parameter will be replaced with. For example:

MyClass myIntClass; // instantiates MyClass with int template argument
MyClass myFloatClass; // instantiates MyClass with float template argument

In this example, two instances of `MyClass` are created with different template arguments.

Template specialization is a feature in C++ that allows you to define a special version of a class template for a specific type. This can be useful when you need to provide a different implementation for a specific type, or when thegeneric implementation of the template is not suitable for a particular type.

To define a specialized version of a class template in C++, we use the following syntax:

template <>
class MyClass {
public:
    char getData() { return data; }
    void setData(char value) { data = value; }

private:
    char data;
};

Here, `MyClass` is the name of the specialized version of the class template, with `` indicating that the template parameter is `char`. The class members provide a specialized implementation for the `char` type.

When you instantiate a class template with a type that has a specialized version, the specialized version will be used instead of the generic version. For example:

MyClass myIntClass; // instantiates the generic version of MyClass
MyClass myCharClass; // instantiates the specialized version of MyClass for char

In this example, the `myIntClass` instance uses the generic version of the `MyClass` template, while the `myCharClass` instance uses the specialized version of the `MyClass` template for `char`.

Template inheritance is a feature in C++ that allows you to define a class template that inherits from another class template. This can be useful when you need to extend the functionality of a generic class template with additional functionality.

To define a class template that inherits from another class template in C++, we use the following syntax:

template
class BaseClass {
public:
    void doSomething(T value) { /* implementation */ }
};

template 
class DerivedClass : public BaseClass {
public:
    void doSomethingElse(U value) { /* implementation */ }
};

Here, `BaseClass` is the name of the base class template, and `DerivedClass` is the name of the derived class template that inherits from `BaseClass`. The `DerivedClass` template parameter (`U`) is used to specify the type of the derived class.

In this example, `DerivedClass` inherits from `BaseClass` and adds a new member function `doSomethingElse()` that takes a parameter of type `U`. The `doSomething()` member function of `BaseClass` is also available in `DerivedClass`.

To instantiate a derived class template, you must specify the template argument for both the base class and derived class. For example:

DerivedClass myDerivedClass; // instantiates DerivedClass with int template argument
myDerivedClass.doSomething(42); // calls doSomething() from BaseClass
myDerivedClass.doSomethingElse(3); // calls doSomethingElse() from DerivedClass

In this example, `myDerivedClass` is an instance of `DerivedClass` with an `int` template argument. The `doSomething()` member function from `BaseClass` is called using the `myDerivedClass` instance, and the `doSomethingElse()` member function from `DerivedClass` is also called using the same instance.

Template inheritance can be used to create a hierarchy of generic classes that can be specialized for different types, while also sharing common functionality. It’s important to use template inheritance judiciously and only when necessary, as it can increase code complexity and make code harder to maintain.