Functions

/*
 FUNCTIONS
 */
func printMessage() {
    let message = "Print this message"
    print(message)
}
printMessage() // Calling function

// ACCEPTING PARAMETERS
func square(number: Int) {
    print(number * number)
}
square(number: 8)

// RETURNING VALUES
func squareOfNumber(number: Int) -> Int {
    return number * number
}
let result = squareOfNumber(number: 8)

// EXTERNAL/INTERNAL PARAMETER NAMES
func sayHello(to name: String) {
    print("Hello, \(name)!")
}
sayHello(to: "Taylor")

func greet(_ person: String) {  // Using _ as external parameter
    print("Hello, \(person)!")
}
greet("Jim")

// DEFAULT PARAMETERS
func studentProgress(name: String, passedTest: Bool = true) {
    if passedTest == true {
        print("\(name) passed the test.")
    } else {
        print("\(name) failed! Boo hoo hoo!")
    }
}
studentProgress(name: "Jane")   // "Jane passed the test."
studentProgress(name: "Greg", passedTest: false) // "Greg failed! Boo hoo hoo!"

// VARIADIC FUNCTIONS
// Function takes in unlimited number of parameters of same type
// and converts them into an array
func squareInput(numbers: Int...) {
    for number in numbers {
        print("\(number) squared is \(number * number)")
    }
}
squareInput(numbers: 2, 4, 6) // "2 squared is 4" etc.

// THROWING FUNCTIONS
// Create enum based on Swift's Error type.
enum PasswordError: Error {
    case obvious
}

// Use "throws" before return type or body of function
func checkPassword(_ password: String) throws -> Bool {
    if password == "password" {
        throw PasswordError.obvious
    }
    return true
}

// Code that might throw an error is called
// within DO block
do {
    try checkPassword("password")   // Error thrown, jumps to CATCH block
    print("That password is good!") // Never executed
} catch {
    print("You can't use that password")
}

// INOUT PARAMETERS
// Place inout before parameter
func doubleInPlace(number: inout Int) {
    number *= 2                 // number = 4
}
var myNum = 2                   // myNum = 2
// Remember & before variable being passed
doubleInPlace(number: &myNum)
print(myNum)                    // myNum = 4