Designing with Swift: Using the Template Method Pattern
As developers, we often find ourselves needing to design and implement a specific set of tasks in a certain order. We can use the Template Method pattern to structure our code in a more maintainable and reusable way. This pattern is especially useful when using the Swift programming language.
The Template Method pattern is a behavioral design pattern that allows us to define the skeleton of an algorithm in a base class, while deferring some of the steps to subclasses. This allows us to easily extend the algorithm without changing the existing code. In this article, we’ll take a look at how to use the Template Method pattern in Swift.
First, let’s consider a simple example. We want to create a system for making coffee. The process for making coffee consists of several steps:
1. Boil the water
2. Grind the coffee beans
3. Add the ground coffee to the boiled water
4. Stir the mixture
5. Pour the coffee into cups
We can use the Template Method pattern to define the overall process for making coffee. We can create a base class that defines the steps for making coffee, and then subclass it to add any additional steps.
Let’s start by creating a CoffeeMakingProcess class. This class will define the template method for making coffee:
class CoffeeMakingProcess {
func makeCoffee() {
boilWater()
grindCoffeeBeans()
addGroundCoffeeToBoiledWater()
stirMixture()
pourCoffeeIntoCups()
}
private func boilWater() {
// Boil the water
}
private func grindCoffeeBeans() {
// Grind the coffee beans
}
private func addGroundCoffeeToBoiledWater() {
// Add the ground coffee to the boiled water
}
private func stirMixture() {
// Stir the mixture
}
private func pourCoffeeIntoCups() {
// Pour the coffee into cups
}
}
As you can see, the makeCoffee() method is the template method. It calls the other methods in the correct order to make coffee. The other methods are all marked as private, so they cannot be overridden by subclasses.
We can now subclass this class to add any additional steps required for a specific type of coffee. For example, let’s say we want to make espresso. We can create a subclass of CoffeeMakingProcess called EspressoMakingProcess:
class EspressoMakingProcess: CoffeeMakingProcess {
override func makeCoffee() {
super.makeCoffee()
addEspressoShot()
}
private func addEspressoShot() {
// Add an espresso shot
}
}
This subclass overrides the makeCoffee() method to call the superclass’s implementation, and then adds an additional step for adding an espresso shot.
We can now use the EspressoMakingProcess class to make espresso:
let espressoMakingProcess = EspressoMakingProcess()
espressoMakingProcess.makeCoffee()
The Template Method pattern is a powerful tool for structuring code in a maintainable and reusable way. It allows us to define the overall flow of an algorithm in a base class, while allowing subclasses to customize the details. This makes it easy to extend the algorithm without changing the existing code.
When using the Swift programming language, it’s important to remember that the Template Method pattern is not available as a built-in language feature. However, it can be implemented using the language’s object-oriented features. By taking advantage of the language’s flexibility, we can easily create a Template Method pattern that is tailored to our specific needs.