In Swift, the @discardableResult attribute is used to indicate that the return value of a function can be ignored and doesn’t need to be used. This is particularly useful when a function has side effects or when you intentionally want to ignore its return value. Let’s illustrate this with a simple example:
class FileManager {
@discardableResult
func openFile(withName name: String) -> Bool {
// Code to open and perform operations on the file
print("Opening file: \(name)")
return true
}
}
let fileManager = FileManager()
fileManager.openFile(withName: "example.txt") // The return value can be ignored
In the code above, the openFile(withName:) function opens a file, performs some operations, and returns true. However, because we may not need to use the return value, we use the @discardableResult attribute to indicate that it’s acceptable to ignore the return value.
Without the @discardableResult attribute, you might receive a compiler warning like this:
Result of call to 'openFile(withName:)' is unused
Using @discardableResult allows you to suppress this warning when you intentionally don’t need to use the return value. However, it’s important to note that you should only use @discardableResult when you genuinely don’t need the return value. If the return value is necessary for your code logic, it’s better not to use the attribute.
Swift Docs includes “discardableResult”