Designing with Swift: Chain of Responsibility Pattern
Swift programming language is a modern, fast, and powerful language. It’s used to create apps for iOS, macOS, watchOS, and tvOS. It can also be used to create powerful applications for the web. One of the most powerful design patterns in Swift is the Chain of Responsibility pattern. It allows us to create complex systems that are easier to maintain and extend.
The Chain of Responsibility pattern is an object-oriented design pattern that allows multiple objects to handle a request. Each object has an opportunity to process the request before it is passed on to the next object in the chain. The requesting object does not need to know which object will handle the request, only that the request will eventually be handled. This makes the system more flexible and extensible.
In this blog post, we’ll look at how to implement the Chain of Responsibility pattern in Swift. We’ll use a simple example of a request to an online store. The request will include the customer’s name and address, and the store will need to validate both the name and address before the request can be processed.
To implement the Chain of Responsibility pattern, we’ll create three classes: RequestHandler, NameValidator, and AddressValidator. The RequestHandler class will act as the base class for the two validator classes. It will contain the logic for passing the request along the chain.
class RequestHandler {
private var nextHandler: RequestHandler?
func setNext(handler: RequestHandler) {
self.nextHandler = handler
}
func processRequest(name: String, address: String) {
if let nextHandler = nextHandler {
nextHandler.processRequest(name: name, address: address)
}
}
}
The NameValidator class will check that the name provided is valid before passing the request along the chain.
class NameValidator: RequestHandler {
override func processRequest(name: String, address: String) {
if isNameValid(name) {
super.processRequest(name: name, address: address)
} else {
print("Name is invalid")
}
}
private func isNameValid(_ name: String) -> Bool {
// Validation code here
}
}
The AddressValidator class will check that the address provided is valid before passing the request along the chain.
class AddressValidator: RequestHandler {
override func processRequest(name: String, address: String) {
if isAddressValid(address) {
super.processRequest(name: name, address: address)
} else {
print("Address is invalid")
}
}
private func isAddressValid(_ address: String) -> Bool {
// Validation code here
}
}
Finally, we’ll create an instance of the NameValidator and AddressValidator classes and set them up in a chain.
let nameValidator = NameValidator()
let addressValidator = AddressValidator()
nameValidator.setNext(handler: addressValidator)
nameValidator.processRequest(name: "John Doe", address: "123 Main Street")
In this example, the request is passed to the NameValidator first. If the name is valid, the request is passed to the AddressValidator. If the address is valid, the request is processed. If either the name or address is invalid, the request is not processed.
The Chain of Responsibility pattern is a powerful design pattern that can be used to create complex systems that are easier to maintain and extend. It allows us to create a chain of objects that can process requests in a specific order. This makes our systems more flexible and extensible.
We’ve seen how to implement the Chain of Responsibility pattern in Swift. We created a RequestHandler class that acts as the base class for the two validator classes. We then created instances of the NameValidator and AddressValidator classes and set them up in a chain. Finally, we processed a request by passing it through the chain of validators.