With extensions, we can add new properties, methods, initializers, subscripts, or make an existing type conform to a protocol. One thing to note is that extensions cannot override existing functionality.
To define an extension, we use the extension
keyword followed by the type that we are extending. The following example shows how we would create an extension that extends the string class:
extension String { //add new functionality here }
Let's see how extensions work by adding a reverse()
method and a firstLetter
property to Swift's standard string class:
extension String { var firstLetter: Character { get { var letters = Array(self) return letters[0] } } func reverse() -> String { var reverse = "" for letter in self { reverse = "\(letter)" + reverse } return reverse } }
When we extend an existing class or structure we define properties, methods, initializers, subscripts, and...