Design Patterns in Swift: Template Method Explained

Design Patterns in Swift: Template Method Explained

Design patterns are an integral part of software development, and Swift is no exception. In this article, we will discuss the Template Method design pattern, which is a behavioral pattern used to provide a consistent structure for subclasses to follow. We will look at the purpose of the template method, when it should be used, and how it can be implemented in Swift.

The Template Method design pattern is a way to define the skeleton of an algorithm in a base class, while allowing subclasses to redefine certain steps of the algorithm without changing its overall structure. This allows us to create a set of subclasses that all share the same core logic, but have the flexibility to customize certain parts of it.

To illustrate this concept, let’s look at an example. Imagine we are creating an app for a restaurant. The restaurant has several different types of meals, such as burgers, salads, and pasta dishes. Each type of meal has its own unique preparation process, but there are also some common steps that are shared across all meals. We could use the Template Method design pattern to create a base Meal class that defines the overall structure of the meal preparation process, and then create subclasses for each type of meal that override certain steps of the process.

The Template Method design pattern is made up of three main components: the template method, the abstract operations, and the concrete operations. The template method defines the overall structure of the algorithm and contains calls to the abstract operations. The abstract operations are defined in the base class and are meant to be overridden by subclasses. The concrete operations are defined in the base class and are not meant to be overridden.

Let’s see how this works in our restaurant example. The template method would contain the overall structure of the meal preparation process, and would call the abstract operations. The abstract operations would define the steps of the process that need to be customized for each type of meal, such as adding the specific ingredients or cooking the food in a certain way. The concrete operations would define the steps of the process that are the same for all meals, such as setting the table or cleaning up afterwards.

Now that we understand the Template Method design pattern, let’s look at how it can be implemented in Swift. To start, we will create a base Meal class that contains the template method. This method will define the overall structure of the meal preparation process and will call the abstract operations.

“`swift
class Meal {
func prepare() {
setTable()
addIngredients()
cookFood()
serveMeal()
cleanUp()
}

func setTable() {
// Set the table
}

func addIngredients() {
// Add the ingredients
}

func cookFood() {
// Cook the food
}

func serveMeal() {
// Serve the meal
}

func cleanUp() {
// Clean up
}
}
“`

Next, we will define the abstract operations in the base class. These methods will be overridden by subclasses in order to customize the meal preparation process for each type of meal.

“`swift
class Meal {
// …

func addIngredients() {
// Abstract method – must be overridden
}

func cookFood() {
// Abstract method – must be overridden
}
}
“`

Finally, we will create subclasses for each type of meal. These subclasses will override the abstract operations in order to customize the meal preparation process for each type of meal.

For example, the Burger subclass could override the addIngredients() and cookFood() methods to add the burger patty and cook it on the grill.

“`swift
class Burger: Meal {
override func addIngredients() {
// Add the burger patty
}

override func cookFood() {
// Cook on the grill
}
}
“`

Similarly, the Salad subclass could override the addIngredients() and cookFood() methods to add the salad ingredients and toss them together.

“`swift
class Salad: Meal {
override func addIngredients() {
// Add the salad ingredients
}

override func cookFood() {
// Toss the salad
}
}
“`

The Template Method design pattern is a great way to create a set of subclasses that all share the same core logic, but have the flexibility to customize certain parts of it. It is especially useful when there is a common structure that needs to be followed, but certain steps of the process need to be customized for each type of object. In Swift, the Template Method design pattern can be implemented using a base class with a template method and abstract operations, and subclasses that override the abstract operations in order to customize the process for each type of object.