Closures - Part II

/*
 CLOSURES - PART TWO
 */

// CLOSURES AS PARAMETERS WHEN THEY ACCEPT PARAMETERS
func travel(action: (String) -> Void) {
    print("I'm getting ready to go")
    action("London")
    print("I have arrived!")
}

travel { (place: String) in
    print("I'm going to \(place) in my car.")
}

// CLOSURES AS PARAMETERS WHEN THEY RETURN VALUES
func travel(action: (String) -> String) {
    print("I'm getting read to go")
    let description = action("Montreal")
    print(description)
    print("I've arrived!")
}

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

// SHORTHAND PARAMETER NAMES

// Swift knows that the above parameter (place: String)
// is a string. So it can be removed:
travel { place -> String in
    return "I'm going to \(place) in my car"
}

// Swift also knows the return type must be a string
travel { place in
    return "I'm going to \(place) in my car"
}

// Since there is only one line of code after "in"
// "return" can be removed.
travel {
    place in
    "I'm going to \(place) in my car"
}

// "place in" can be replaced by automatic names for closure parameters:
travel {
    "I'm going to \($0) un my car"
}

// CLOSURES WITH MULTIPLE PARAMETERS
// The following function has a closure as a parameter
// that itself accepts two parameters:
func travel(action: (String, Int) -> String) {
    print("I'm getting ready to go.")
    let description = action("London", 60)
    print(description)
    print("I arrived!")
}

// Full syntax call:
travel { (location: String, speed: Int) -> String in
    return "I'm going to \(location) at \(speed) miles per hour."
}

// Swift knows the type of the parameters, so they can be removed
travel { location, speed -> String in
    return "I'm going to \(location) at \(speed) miles per hour."
}

// Swift knows the return type, so it can be removed:
travel { location, speed in
    return "I'm going to \(location) at \(speed) miles per hour."
}

// Since there is only one line of code after "in," "return" can be removed:
travel { location, speed in
    return "I'm going to \(location) at \(speed) miles per hour."
}

// "location, speed in" can be replaced by automatic parameters:
travel {
    "I'm going to \($0) at \($1) miles per hour."
}

// RETURNING CLOSURES FROM FUNCTIONS
// The following function will return a closure
// that is called by a string
// but (the closure) returns void
func travel() -> (String) -> Void {
    var counter = 1
    return {
        print("\(counter). I'm going to \($0)")
        counter += 1
    }
}

// Call function to get closure
// Then call that closure with string "LA"
let result = travel()
result("LA")    // counter = 1

// CAPTURING VALUES
// "counter" variable was created within travel()
// and is captured by the closure each time and
// will remain alive for that closure.
result("London")    // counter = 2
result("Montreal")  // counter = 3