How using an "Optional Pattern" alongside an "Enumeration Case Pattern" in Swift reduces the code it takes to match an optional AND an enum case at once while capturing its associated values.

LocalAuthentication.swift

// MARK: - guard without Optional Pattern

extension LocalAuthentication {
    
    convenience init?(authenticationLevel: AuthenticationLevel?){
        guard let authenticationLevel = authenticationLevel else {
            return nil
        }
        
        switch authenticationLevel {
        case .AuthenticationLevelZero(let mobile, let deviceId, _):
            self.init(deviceConfiguration: DeviceConfiguration(deviceId: deviceId), mobile: mobile)
        default:
            return nil
        }
    }
}

// MARK: - guard with Optional Pattern

extension LocalAuthentication {

convenience init?(authenticationLevel: AuthenticationLevel?){
        guard case let .AuthenticationLevelZero(mobile, deviceId, _)? = authenticationLevel else {
            return nil
        }

        self.init(deviceConfiguration: DeviceConfiguration(deviceId: deviceId), mobile: mobile)
    }
}

The requirement is to create a LocalAuthentication instance only if the given AuthenticationLevel (an enum) is AuthenticationLevelZero while also getting its associated values.

Ref: https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/enum-case-pattern