Error protocol conformance in Swift - Mini Project: Build & Apply

Error Protocol Conformance in Swift

📖 Scenario: Imagine you are building a simple app that checks user input and reports errors clearly.

🎯 Goal: You will create a custom error type by conforming to the Error protocol, then use it to handle errors in a function.

📋 What You'll Learn

Create an enum called InputError that conforms to the Error protocol

Add two cases to InputError: empty and tooShort

Write a function validateInput(_ input: String) throws that throws InputError.empty if the input is empty

Throw InputError.tooShort if the input length is less than 5 characters

Use a do-catch block to call validateInput and print appropriate messages for each error

💡 Why This Matters

🌍 Real World

Custom error types help apps give clear feedback when something goes wrong, like invalid user input.

💼 Career

Understanding error handling is essential for writing safe and user-friendly Swift applications.

1

Create the InputError enum conforming to Error

Create an enum called InputError that conforms to the Error protocol. Add two cases: empty and tooShort.

Swift

// Your code here

Need a hint?

Use enum InputError: Error to start. Add case empty and case tooShort inside.

2

Write the validateInput function that throws errors

Write a function called validateInput(_ input: String) throws. Inside, throw InputError.empty if input is empty. Throw InputError.tooShort if input.count is less than 5.

Swift

enum InputError: Error {
    case empty
    case tooShort
}

// Your code here

Need a hint?

Use if input.isEmpty to check empty. Use throw InputError.empty inside. Then check input.count < 5 and throw InputError.tooShort.

3

Use do-catch to handle errors from validateInput

Write a do-catch block that calls try validateInput(input) with input set to "Hi". Catch InputError.empty and print "Input is empty". Catch InputError.tooShort and print "Input is too short". Catch any other errors and print "Unknown error".

Swift

enum InputError: Error {
    case empty
    case tooShort
}

func validateInput(_ input: String) throws {
    if input.isEmpty {
        throw InputError.empty
    }
    if input.count < 5 {
        throw InputError.tooShort
    }
}

// Your code here

Need a hint?

Use do { try validateInput(input) } and multiple catch blocks for each error case. Print messages inside each catch.

4

Print the final output

Run the program and print the output from the do-catch block.

Swift

enum InputError: Error {
    case empty
    case tooShort
}

func validateInput(_ input: String) throws {
    if input.isEmpty {
        throw InputError.empty
    }
    if input.count < 5 {
        throw InputError.tooShort
    }
}

let input = "Hi"
do {
    try validateInput(input)
    print("Input is valid")
} catch InputError.empty {
    print("Input is empty")
} catch InputError.tooShort {
    print("Input is too short")
} catch {
    print("Unknown error")
}

// Your code here

Need a hint?

The output should be Input is too short because "Hi" has less than 5 characters.