#1 SOLID - Single Responsibility Principle | Swift | iOS Development

#ios #swift

SRP state that a class should have only one reason to change.

Below is an implementation for a Debt calculator.

public class DebtCalculatorOld {

    private var totalDebt: Int = 0

    public init(totalCalories: Int = 0) {
        self.totalDebt = totalCalories
    }

    public func update(_ amount: Int) {
        self.totalDebt += amount

        if self.totalDebt > 500 {
            //Notify user about the change
            print("Limit Reached")
        }
    }
}

Each class should focus on performing a single task.
The below class is for managing debt of a user. If the total debt reaches a certain amount then we should notify the user about it.
Here we have added everything in one class which not recommended as per single responsibility principle.
In future, if we want to change the notification type to be email. Then we will have to change the update function in the DebtCalculator.
There should not be multiple reasons for a class to change.

public class DebtCalculator {

    private var totalDebt: Int = 0
    private var notificationManager: NotificationManager

    public init(totalCalories: Int = 0,
                notificationManager: NotificationManager = NotificationManager()) {
        self.totalDebt = totalCalories
        self.notificationManager = notificationManager
    }

    public func update(_ amount: Int) {
        self.totalDebt += amount

        if self.totalDebt > 500 {
            notificationManager.notify(totalDebt)
        }
    }
}

public class NotificationManager {

    public init() {}

    func notify(_ current: Int) {
        print("Limit Reached - \(current)")
    }
}

Here we have seperate class for Adding debt releated features and Notification releated features.
In future if we want to chagne the Notification type to email we can change it without making changes in DebtCalculator