Declare a variable or constant that conforms to a protocol in Swift

Question

In Swift how do you declare a variable (or constant) that conforms to a protocol?

I've tried

let whatever: protocol <myProtocol>

and

let whatever: myProtocol

But when setting it I get the error

Cannot convert the expression's type '()' to type 'myProtocol'

Answer 1

There is no such necessary to do such thing, because when you declare the type of your variable (or constant), it should be known if it is conforming a protocol or not. But in case sometimes you are using legacy objc id, you may get an AnyObject. In that situation, you can just do a downcast to convert it as a protocol type and use it.

let whatever: AnyObject = someObj
let conformProtocol = whatever as myProtocol

conformProtocol.callMethod()

Or you may want to use as? for a safer converting.