**Course Title:** Swift Programming: From Basics to Advanced Development **Section Title:** Protocols and Protocol-Oriented Programming **Topic:** Build a program utilizing protocols and protocol extensions. **Objective:** In this lab, you'll design and implement a simple banking system using protocols and protocol extensions in Swift. By the end of this lab, you'll be able to create and apply protocols to design flexible systems that can be easily extended. **Introduction** In the previous sections, we've explored the basics of protocols and protocol extensions. Now, it's time to put this knowledge into practice by building a real-world program. **Lab Overview** In this lab, we'll create a simple banking system with two account types: Checking and Savings. We'll define a protocol `Account` to specify the common requirements for both account types. Then, we'll create two structs, `CheckingAccount` and `SavingsAccount`, that adopt the `Account` protocol. We'll also use protocol extensions to add default implementations for some of the protocol requirements. **Step 1: Define the `Account` Protocol** Create a new Playground in Xcode and add the following code: ```swift // Define the Account protocol protocol Account { var accountNumber: String { get set } var balance: Double { get set } func deposit(amount: Double) func withdraw(amount: Double) func displayAccountInfo() } ``` This protocol defines the common requirements for any account type, including an account number, balance, deposit, withdrawal, and display account information. **Step 2: Create the `CheckingAccount` Struct** Add the following code to create a `CheckingAccount` struct that adopts the `Account` protocol: ```swift // Create the CheckingAccount struct struct CheckingAccount: Account { var accountNumber: String var balance: Double func deposit(amount: Double) { balance += amount } func withdraw(amount: Double) { if balance >= amount { balance -= amount } else { print("Insufficient funds") } } func displayAccountInfo() { print("Account Number: \(accountNumber)") print("Balance: \(balance)") } } ``` **Step 3: Create the `SavingsAccount` Struct** Add the following code to create a `SavingsAccount` struct that adopts the `Account` protocol: ```swift // Create the SavingsAccount struct struct SavingsAccount: Account { var accountNumber: String var balance: Double var interestRate: Double func deposit(amount: Double) { balance += amount } func withdraw(amount: Double) { if balance >= amount { balance -= amount } else { print("Insufficient funds") } } func displayAccountInfo() { print("Account Number: \(accountNumber)") print("Balance: \(balance)") print("Interest Rate: \(interestRate)%") } } ``` **Step 4: Add Protocol Extensions** Add the following code to add default implementations for the `deposit` and `withdraw` methods using protocol extensions: ```swift // Add protocol extensions for default implementations extension Account { mutating func deposit(amount: Double) { balance += amount } mutating func withdraw(amount: Double) { if balance >= amount { balance -= amount } else { print("Insufficient funds") } } } ``` **Step 5: Test the Program** Create instances of `CheckingAccount` and `SavingsAccount` and test the program: ```swift // Test the program var checkingAccount = CheckingAccount(accountNumber: "1234567890", balance: 1000.0) var savingsAccount = SavingsAccount(accountNumber: "9876543210", balance: 500.0, interestRate: 2.0) checkingAccount.displayAccountInfo() savingsAccount.displayAccountInfo() checkingAccount.deposit(amount: 500.0) savingsAccount.deposit(amount: 200.0) checkingAccount.displayAccountInfo() savingsAccount.displayAccountInfo() checkingAccount.withdraw(amount: 200.0) savingsAccount.withdraw(amount: 100.0) checkingAccount.displayAccountInfo() savingsAccount.displayAccountInfo() ``` **Conclusion** In this lab, you've designed and implemented a simple banking system using protocols and protocol extensions in Swift. You've seen how protocols can be used to define common requirements for different account types and how protocol extensions can be used to add default implementations for some of the protocol requirements. **Key Takeaways** * Define protocols to specify common requirements for different types. * Use protocol extensions to add default implementations for some of the protocol requirements. * Adopt protocols in structs and classes to design flexible systems. **External Resources** * [Swift Documentation: Protocols](https://docs.swift.org/swift-book/LanguageGuide/Protocols.html) * [Swift Documentation: Protocol Extensions](https://docs.swift.org/swift-book/LanguageGuide/Protocols.html#ID521) **Leave a Comment/Ask for Help** If you have any questions or need help with this lab, please leave a comment below.