Design Patterns: Prox in Swift – Harness the Power of Reusability
Design patterns are one of the most important concepts in software engineering. They allow us to write code that is reusable, maintainable, and extensible. In this blog post, we’ll explore one of the most popular design patterns, Proxy, and how it can be implemented in Swift.
Proxy is a design pattern that allows us to intercept calls to an object and modify them before they reach the target object. It’s a very powerful technique and can be used for a variety of tasks such as caching, logging, authentication, and more.
Let’s start by looking at an example. We’ll create a simple class called `Calculator` that has two methods: `add` and `subtract`. The `add` method takes two integers and adds them together, while the `subtract` method takes two integers and subtracts the second from the first.
“`swift
class Calculator {
func add(a: Int, b: Int) -> Int {
return a + b
}
func subtract(a: Int, b: Int) -> Int {
return a – b
}
}
“`
Now, let’s say we want to log every call to the `Calculator` class. We could do this by modifying the `add` and `subtract` methods to log their arguments and results. However, this would mean that we’d have to modify the `Calculator` class whenever we wanted to add or remove logging.
This is where the Proxy pattern comes in. We can create a `LoggingProxy` class that wraps the `Calculator` class and logs every call to its methods. This way, we can keep the logging code separate from the `Calculator` class and add or remove logging without touching the `Calculator` class.
“`swift
class LoggingProxy: Calculator {
private let calculator = Calculator()
override func add(a: Int, b: Int) -> Int {
print(“Adding \(a) and \(b)”)
let result = calculator.add(a: a, b: b)
print(“Result: \(result)”)
return result
}
override func subtract(a: Int, b: Int) -> Int {
print(“Subtracting \(b) from \(a)”)
let result = calculator.subtract(a: a, b: b)
print(“Result: \(result)”)
return result
}
}
“`
As you can see, the `LoggingProxy` class wraps the `Calculator` class and overrides its methods. Whenever a method is called, the `LoggingProxy` class logs the arguments and result before passing the call to the `Calculator` class. This way, we can easily add or remove logging without having to modify the `Calculator` class.
Proxy is a powerful pattern that can be used to add extra functionality to an existing class without having to modify it. It’s especially useful for tasks such as logging, authentication, caching, and more. In this blog post, we’ve seen how to implement the Proxy pattern in Swift and use it to add logging to an existing class. By harnessing the power of reusability, we can easily extend our code without having to modify the original class.