###
//: ## Functions and Closures
//:
//: Use `func` to declare a function. Call a function by following its name with a list of arguments in parentheses. Use `->` to separate the parameter names and types from the function’s return type.
//:
func greet(name: String, day: String) -> String {
return "Hello \(name), today is \(day)."
}
greet("Bob", day: "Tuesday")
//: > **Experiment**:
//: > Remove the `day` parameter. Add a parameter to include today’s lunch special in the greeting.
//:
//: Use a tuple to make a compound value—for example, to return multiple values from a function. The elements of a tuple can be referred to either by name or by number.
//:
func calculateStatistics(scores: [Int]) -> (min: Int, max: Int, sum: Int) {
var min = scores[0]
var max = scores[0]
var sum = 0
for score in scores {
if score > max {
max = score
} else if score < min {
min = score
}
sum += score
}
return (min, max, sum)
}
let statistics = calculateStatistics([5, 3, 100, 3, 9])
print(statistics.sum)
print(statistics.2)
//: Functions can also take a variable number of arguments, collecting them into an array.
//:
func sumOf(numbers: Int...) -> Int {
var sum = 0
for number in numbers {
sum += number
}
return sum
}
sumOf()
sumOf(42, 597, 12)
//: > **Experiment**:
//: > Write a function that calculates the average of its arguments.
//:
//: Functions can be nested. Nested functions have access to variables that were declared in the outer function. You can use nested functions to organize the code in a function that is long or complex.
//:
func returnFifteen() -> Int {
var y = 10
func add() {
y += 5
}
add()
return y
}
returnFifteen()
//: Functions are a first-class type. This means that a function can return another function as its value.
//:
func makeIncrementer() -> (Int -> Int) {
func addOne(number: Int) -> Int {
return 1 + number
}
return addOne
}
var increment = makeIncrementer()
increment(7)
//: A function can take another function as one of its arguments.
//:
func hasAnyMatches(list: [Int], condition: Int -> Bool) -> Bool {
for item in list {
if condition(item) {
return true
}
}
return false
}
func lessThanTen(number: Int) -> Bool {
return number < 10
}
var numbers = [20, 19, 7, 12]
hasAnyMatches(numbers, condition: lessThanTen)
//: Functions are actually a special case of closures: blocks of code that can be called later. The code in a closure has access to things like variables and functions that were available in the scope where the closure was created, even if the closure is in a different scope when it is executed—you saw an example of this already with nested functions. You can write a closure without a name by surrounding code with braces (`{}`). Use `in` to separate the arguments and return type from the body.
//:
numbers.map({
(number: Int) -> Int in
let result = 3 * number
return result
})
//: > **Experiment**:
//: > Rewrite the closure to return zero for all odd numbers.
//:
//: You have several options for writing closures more concisely. When a closure’s type is already known, such as the callback for a delegate, you can omit the type of its parameters, its return type, or both. Single statement closures implicitly return the value of their only statement.
//:
let mappedNumbers = numbers.map({ number in 3 * number })
print(mappedNumbers)
//: You can refer to parameters by number instead of by name—this approach is especially useful in very short closures. A closure passed as the last argument to a function can appear immediately after the parentheses. When a closure is the only argument to a function, you can omit the parentheses entirely.
//:
let sortedNumbers = numbers.sort { $0 > $1 }
print(sortedNumbers)
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