Handling empty and nil Strings in Swift compared to Java

NullEmptyStringDemo.java

public class NullEmptyStringDemo {
    public static void main(String[] args) {
        ApiClient apiClient = new ApiClient();

        // throws IllegalArgumentException, but note that we don't have to catch it
        apiClient.getItemAsync("", "");
    }

    public static class ApiClient {
        // Simulate a similar call in ApiClient
        public void getItemAsync(String id, String userId /* other parameters */) {
            if ( id == null || id.isEmpty() ) {
                throw new IllegalArgumentException("id");
            }

            if ( userId == null || userId.isEmpty() ) {
                throw new IllegalArgumentException("userId");
            }

            // Do stuff
        }
        
    }

}

NullEmptyStringDemoPlayground.swift

//: Playground - noun: a place where people can play

// An example error type that could be used when we need to throw an error an empty string
enum StringError: ErrorType {
    case EmptyString(variableName: String)
}

//
// OPTION 1: ApiClient with guard statements
//

public class ApiClientWithThrows {
    // A trimmed down version of the getItemAsync method from ApiClient
    public func getItemAsync(id: String, userId: String /* Other params */) throws {
        guard !id.isEmpty else {
            throw StringError.EmptyString(variableName: "id")
        }
        
        guard !userId.isEmpty else {
            throw StringError.EmptyString(variableName: "userId")
        }
    
        print("Users/\(id)/Items/\(userId)")
    }
}

//
// OPTION 1: Simulate caller
//

public class Caller {
    let apiClient = ApiClientWithThrows()
    
    public func callApiClient(id: String, userId: String) {
        do {
            try apiClient.getItemAsync(id, userId: userId)
        } catch StringError.EmptyString(let variableName) {
            print("found empty string for \(variableName)")
        } catch {
            // This catch is needed if we do not want to declare 'callApiClient' with throws
            print("Exhaust all options")
        }

        print("Other code")
    }
}

let caller = Caller()
caller.callApiClient("", userId: "")
// Prints: found empty string for id
// Prints: Other code

//
// OPTION 2: ApiClient without guard statements, assuming Strings created with extension
//

public class ApiClientWithoutThrows {
    // A trimmed down version of the getItemAsync method from ApiClient
    public func getItemAsync(id: String, userId: String /* Other params */) {
        print("Users/\(id)/Items/\(userId)")
    }
}

//
// OPTION 2: Simulate caller using String extension with failable
//

extension String {
    init!(nonEmptyString: String) {
        if nonEmptyString.isEmpty { return nil }
        self.init(nonEmptyString)
    }
}

public class CallerWithString {
    let apiClient = ApiClientWithoutThrows()
    
    public func callApiClient(id: String, userId: String) {
        apiClient.getItemAsync(id, userId: userId)
        
        print("Other code")
    }
}

let callerWithString = CallerWithString()

let id = String(nonEmptyString: "")
let userId = String(nonEmptyString: "dd")

// call fails with fatal error: unexpectedly found nil while unwrapping an Optional value
callerWithString.callApiClient(id, userId: userId)