Using closures as parameters when they return values

We’ve been using () -> Void to mean “accepts no parameters and returns nothing”, but you can replace that Void with any type of data to force the closure to return a value.

To demonstrate this, we can write a travel() function that accepts a closure as its only parameter, and that closure in turn accepts a string and returns a string:

func travel(action: (String) -> String) {
    print("I'm getting ready to go.")
    let description = action("London")
    print(description)
    print("I arrived!")
}

Now when we call travel() using trailing closure syntax, our closure code is required to accept a string and return a string:

travel { (place: String) -> String in
    return "I'm going to \(place) in my car"
}

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