CodeToLive

Error Handling in Swift

Swift provides several ways to handle errors, including throwing functions and the Result type.

Defining Errors

enum NetworkError: Error {
    case invalidURL
    case timeout
    case serverError(status: Int)
}

Throwing Functions

func fetchData(from urlString: String) throws -> Data {
    guard let url = URL(string: urlString) else {
        throw NetworkError.invalidURL
    }
    // ... fetch data
}

Do-Try-Catch

do {
    let data = try fetchData(from: "https://example.com")
    print("Data received")
} catch NetworkError.invalidURL {
    print("Invalid URL")
} catch {
    print("Other error: \(error)")
}

Try? and Try!

let data1 = try? fetchData(from: "badurl")  // nil on error
let data2 = try! fetchData(from: "goodurl")  // Crash on error

Result Type

func fetchDataResult(from url: String) -> Result<Data, NetworkError> {
    guard URL(string: url) != nil else {
        return .failure(.invalidURL)
    }
    // ... return .success(data)
}

switch fetchDataResult(from: "https://example.com") {
case .success(let data):
    print("Data: \(data)")
case .failure(let error):
    print("Error: \(error)")
}

Assertions

let age = -3
assert(age >= 0, "Age can't be negative")  // Debug builds only
precondition(age >= 0, "Age can't be negative")  // All builds

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