What does an ampersand (&) mean in the Swift language?

Question

I know about the ampersand as a bit operation but sometimes I see it in front of variable names. What does putting an & in front of variables do?

Answer 1

There's another function of the ampersand in the Swift language that hasn't been mentioned yet. Take the following example:

protocol Foo {}
protocol Bar {}

func myMethod(myVar: Foo & Bar) {
    // Do something
}

Here the ampersand syntax is stating that myVar conforms to both the Foo and Bar protocol.

As another use case, consider the following:

func myMethod() -> UIViewController & UITableViewDataSource {
    // Do something
}

Here we're saying that the method returns a class instance (of UIViewController) that conforms to a certain protocol (UITableViewDataSource). This is rendered somewhat obsolete with Swift 5.1's Opaque Types but you may see this syntax in pre-Swift 5.1 code from time to time.