Try? for optional result in Swift - Mini Project: Build & Apply

Using try? for Optional Result in Swift

📖 Scenario: Imagine you are building a simple app that reads numbers from text inputs and converts them to integers. Sometimes the input might not be a valid number, and you want to handle this safely without crashing the app.

🎯 Goal: You will learn how to use try? in Swift to safely attempt an operation that might fail and get an optional result instead of a crash.

📋 What You'll Learn

Create a function that throws an error if the input string is not a valid number

Use try? to call this function and get an optional integer

Print the optional result to see if the conversion succeeded or failed

💡 Why This Matters

🌍 Real World

Apps often need to convert user input to numbers safely. Using <code>try?</code> helps avoid crashes when input is invalid.

💼 Career

Understanding error handling and optionals is essential for Swift developers building robust iOS apps.

1

Create a throwing function to convert string to integer

Write a function called convertToInt that takes a String parameter named input and returns an Int. The function should throw an error if the string cannot be converted to an integer. Define an enum ConversionError with a case invalidNumber to represent this error.

Swift

enum ConversionError: Error {
    // Define error case here
}

func convertToInt(input: String) throws -> Int {
    // Your code here
}

Need a hint?

Use Int(input) to try converting the string. If it fails, throw ConversionError.invalidNumber.

2

Use try? to call the throwing function safely

Create a constant called result and assign it the value of calling convertToInt with the string "123" using try? to handle the error as an optional.

Swift

enum ConversionError: Error {
    case invalidNumber
}

func convertToInt(input: String) throws -> Int {
    if let number = Int(input) {
        return number
    } else {
        throw ConversionError.invalidNumber
    }
}

// Use try? to call convertToInt with "123"
// Your code here

Need a hint?

Use let result = try? convertToInt(input: "123") to get an optional integer.

3

Try converting an invalid string with try?

Create a constant called invalidResult and assign it the value of calling convertToInt with the string "abc" using try?.

Swift

enum ConversionError: Error {
    case invalidNumber
}

func convertToInt(input: String) throws -> Int {
    if let number = Int(input) {
        return number
    } else {
        throw ConversionError.invalidNumber
    }
}

let result = try? convertToInt(input: "123")

// Use try? to call convertToInt with "abc"
// Your code here

Need a hint?

Use let invalidResult = try? convertToInt(input: "abc") to get nil for invalid input.

4

Print the optional results

Print the values of result and invalidResult using print statements to see the optional results.

Swift

enum ConversionError: Error {
    case invalidNumber
}

func convertToInt(input: String) throws -> Int {
    if let number = Int(input) {
        return number
    } else {
        throw ConversionError.invalidNumber
    }
}

let result = try? convertToInt(input: "123")
let invalidResult = try? convertToInt(input: "abc")

// Print result and invalidResult
// Your code here

Need a hint?

Use print(result) and print(invalidResult) to see the optional values.