The @discardableResult Attribute in Swift

Swift has several small features as a language, many of them being neglected quite often while they consist of small programming gems. One of them is the @discardableResult attribute that everybody wish they knew from the beginning.

What’s the purpose of @discardableResult? Put in simple words, when used to annotate a method, then the returned value of the method can be ignored when it gets called.

Let’s make that clear through a basic example. Say that we have the following method that stores the text given as first argument to the file name provided as second argument:

func save(text: String, to file: String) -> Bool {
    do {
        guard let docDirURL =
                FileManager.default.urls(for: .documentDirectory,
                                         in: .userDomainMask).first
        else { return false }
        
        let saveURL = docDirURL
            .appendingPathComponent(file)
            .appendingPathExtension("txt")
        
        try text.write(to: saveURL,
                       atomically: true,
                       encoding: .utf8)
        return true
    }
    catch {
        return false
    }
}

This method does nothing more than simply getting the URL to the documents directory, composing the final URL including the file name and the .txt extension, and…