Warning and error diagnostic directives
Warning and error diagnostic directives 관련
Available from Swift 4.2
SE-0196 (apple/swift-evolution) introduced new compiler directives that help us mark issues in our code. These will be familiar to any developers who had used Objective-C previously, but as of Swift 4.2 we can enjoy them in Swift too.
The two new directives are #warning and #error: the former will force Xcode to issue a warning when building your code, and the latter will issue a compile error so your code won’t build at all. Both of these are useful for different reasons:
#warningis mainly useful as a reminder to yourself or others that some work is incomplete. Xcode templates often use#warningto mark method stubs that you should replace with your own code.#erroris mainly useful if you ship a library that requires other developers to provide some data. For example, an authentication key for a web API – you want users to include their own key, so using#errorwill force them to change that code before continuing.
Both of these work in the same way: #warning("Some message") and #error("Some message"). For example:
func encrypt(_ string: String, with password: String) -> String {
#warning("This is terrible method of encryption")
return password + String(string.reversed()) + password
}
struct Configuration {
var apiKey: String {
#error("Please enter your API key below then delete this line.")
return "Enter your key here"
}
}
Both #warning and #error work alongside the existing #if compiler directive, and will only be triggered if the condition being evaluated is true. For example:
#if os(macOS)
#error("MyLibrary is not supported on macOS.")
#endif
Other Changes in Swift 4.2