Template Method Design Pattern in C++

The Template Method Design Pattern is a way to set up a common process that can be shared by different classes. It gives a main method called the template method that explains the steps to complete a task. Other classes can then fill in the details for some of those steps in their own way, without changing the main process. This helps in reusing code and keeping things simple as well as consistent.

This pattern is helpful when you have a task that follows the same steps every time, but a few steps might need to be done differently. You can keep the main steps in one place and let other classes change only the parts they need. This makes the program easy to read and simple to manage.

For example, think of a program that shows how to prepare a meal. The template method might describe the main steps : gathering ingredients, cooking, and serving. Now, other classes can change how these steps are done to make different meals like breakfast, lunch, or dinner. The main idea stays the same, but each meal can have its own special details.

Key Parts of the Template Method Design Pattern

The Template Method Design Pattern has following components that work together −

• The Abstract Class is the main class that defines the overall process. It includes the template method, which lists all the steps in order. Some steps may already have code, while others are left empty so other classes can fill them in later.
• The Template Method is the main method that shows how the task should be done from start to finish. It calls smaller methods for each step. Some of those smaller methods might be complete, and some might be waiting for other classes to finish them.
• The Concrete Subclasses are the classes that come from the abstract class. They complete the unfinished steps by adding their own code. Each subclass can do things a little differently, but they all still follow the main process written in the template method.
• The Hook Methods are optional steps that can be changed if needed. They let you add or skip small actions without touching the main process. Think of them like little switches you can turn on or off to change small parts of how things work.

C++ Implementation of the Template Method Design Pattern

Let's learn how to use the Template Method pattern in C++ with a simple example. We'll make a program that shows how to prepare different kinds of meals by following the same main steps.

Steps to use the Template Method pattern in C++

Following are the steps to implement the Template Method Design Pattern in C++

• First, make an abstract class that has one main method called the template method. This method lists all the steps of the process, like a recipe. Some steps will already have code, and others will be left empty so that other classes can fill them in later.
• Next, create subclasses that come from the abstract class. These classes will fill in the missing steps with their own code. For example, one class can show how to make breakfast, another one can show how to make lunch, and another one can show how to make dinner.
• Finally, use these subclasses to run the template method. The main steps stay the same, but each subclass adds its own little changes to make the meal special in its own way.

This way, you can keep the main process in one place and still make it easy to add new meal types later without changing the whole program.

C++ Code to Implement Template Method Design Pattern