Question

Give the definition of a template class called HeterogeneousPair that is like the class template Pair discussed in the section "Syntax for Class Templates," except that with HeterogeneousPair the first and second positions may store values of different types. Use two type parameters T1 and \(\mathrm{T} 2 ;\) all items in the first position will be of type \(\mathrm{T} 1\), and all items in the second position will be of type \(T 2 .\) The single mutator method set_element in the template class Pair should be replaced by two mutator methods called set_first and set_second in the template class HeterogeneousPair, Similarly, the single accessor method get_element in the template class Pair should be replaced by two accessor methods called get_first and get_second in the template class HeterogeneousPair.

Short answer

**Answer:** The main differences between the `Pair` and `HeterogeneousPair` class templates are: 1. `Pair` class template has a single type parameter, while `HeterogeneousPair` has two type parameters (T1 and T2), which allows it to handle different data types for its two elements. 2. In the `HeterogeneousPair` class template, separate accessor and mutator methods (get_first, get_second, set_first, and set_second) are implemented for each element, as opposed to a single accessor and mutator in the `Pair` class template. This is necessary to handle the different types for each element.

Step-by-step solution

1. Declare the HeterogeneousPair template class and its private members

First, we'll declare the HeterogeneousPair template class with two type parameters, T1 and T2, and define the private members as "first" of type T1 and "second" of type T2. ```cpp template class HeterogeneousPair { private: T1 first; T2 second; }; ```

2. Implement the set_first and set_second mutator methods

Next, we'll implement the set_first and set_second mutator methods, which accept parameters of type T1 and T2, respectively, and set the value of the corresponding private members. ```cpp template class HeterogeneousPair { private: T1 first; T2 second; public: void set_first(const T1& value) { first = value; } void set_second(const T2& value) { second = value; } }; ```

3. Implement the get_first and get_second accessor methods

Finally, we'll implement the get_first and get_second accessor methods, which return the values of the private members "first" and "second", respectively. Don't forget to mark these methods as const as they are not modifying the data members. ```cpp template class HeterogeneousPair { private: T1 first; T2 second; public: void set_first(const T1& value) { first = value; } void set_second(const T2& value) { second = value; } T1 get_first() const { return first; } T2 get_second() const { return second; } }; ``` This is the complete HeterogeneousPair template class that meets the requirements of the given exercise.

Key concepts

Template Class Definition

In C++, a template class is a blueprint for creating a generic data type. A template class allows you to define a class with parameters for the types of its data members, methods, or even base classes. When you create an instance of this class, you specify what types should replace these parameters. This makes the template class flexible and reusable for various data types.

For instance, when you're dealing with a pair of values that could be of any type, like an integer and a string, instead of writing separate classes for each possible combination, you use a template class to handle them all. The exercise asks for a HeterogeneousPair template class to encapsulate a pair of values of potentially different types, which is a perfect example of the power and utility of template classes in C++.

C++ Class Templates

C++ class templates extend the concept of templates to classes. Think of them as an overarching class framework that can operate with any data type. Rather than defining multiple classes for similar functionality, class templates allow for the definition of a single class that can handle multiple data types.

The HeterogeneousPair discussed in the exercise is an example of such a class template. It uses two type parameters, T1 and T2, to represent two potentially different data types. By specifying these types when creating an instance of HeterogeneousPair, the same class definition can be used to store and manage pairs of integers, strings, or even custom objects.

Mutator and Accessor Methods

The mutator and accessor methods are pivotal for maintaining the integrity of object-oriented programming. Mutator methods, often called 'setters,' allow the modification of private data members of a class. They are critical in controlling how data is changed, ensuring it remains valid and consistent. In the HeterogeneousPair, the mutator methods are set_first and set_second, responsible for setting the values of the first and second data members.

Conversely, accessor methods, known as 'getters,' provide a way to access these private data members without altering them. They are a secure gateway to read the object's state. In our HeterogeneousPair, these methods are get_first and get_second, which return the current values of the pair's components. By separating these mechanisms, you ensure a class is used as intended, encapsulating the internal state and maintaining control over data.