Template Design Pattern in C#

We will now explain the Template Method Pattern. Like the Strategy Pattern, this pattern is part of the behavioral design patterns. As the name Template suggests, we know a template is a kind of layout available for some kind of process, that we can modify as needed and use it. The case here is similar. We have some sub-tasks to complete a big task, that we can use as per our situation requirements. So technically speaking, we make the sub-tasks as abstract and implement them, as per our needs, in different cases. But one thing remains common;  the overall steps of the entire procedure or the algorithm, in other words first Step 1, then Step 2, then Step 3 and so on, that remain the same in their execution order.

Let's explain this concept in detail now.

What the Template Method Pattern is

According to the GoF's definition, this pattern:

Defines the skeleton of an algorithm in an operation, deferring some steps to sub-classes. The Template Method lets sub-classes redefine certain steps of an algorithm without changing the algorithm's structure.

A real-world example

An organization goes to colleges and hires beginner. They have a number of steps defined for the process of hiring in the following order:

Step 1: Take a test in the first round
Step 2: Group discussion in the second round
Step 3: Technical interview
Step 4: HR interview

They have a common process of group discussions and HR interviews for all the departments, but a different test and technical interview process, depending on whether it is for computer or electronics departments. So we create a hiring process template that can be used by the company for two different departments.

Let's convert the preceding real-world example into technical code.

We will be dividing the system into the following components for our implementation of this pattern:

1. Abstract Class: This will be an abstract class, that will have the abstract methods of our technical and test rounds, that will be implemented in the sub-classes based on the departments and the non-abstract methods of the group discussion and the HR rounds.
   
   Most importantly, this class will contain a Non Abstract method that will be calling the abstract methods or any other method defined in this class, to outline the flow of the overall process in a step-wise call to these methods, or you can say, it will contain the sequence of an algorithm.
    
2. Concrete Classes: These will be concrete implementations of our abstract steps of the tests and technical interviews, depending on the departments.

So our initial code setup for defining the template of the hiring process will be like the following:

We will next be implementing the template, to define the test and technical interview rounds, based on the type of department as in the following:

So now we have set up the complete process of hiring for two different departments, with a few common steps. Now we just need to start with the interview process for both the departments, using the client code. So we begin the process with the following code implementation:

So this was all about the Template Method Pattern. For more design patterns, you can check out here.