A Swift Tour (3)

Functions and Closures

Use func to declare a function, call the function by using the parameter list of parentheses, and use --> to separate the return type, parameter name, and type of the function. For example:

Func greet (name: String, day: String)-> String {return "Hello \ (name), today is \ (day ). "} greet (" Bob ", day:" Tuesday ") // This is the call method in the swift document, but I always report an error when writing it in xcode6, so the following greet ("Bob", day: "Tuesday") // This method will not be wrong.

Using a single tuple, a function can return multiple values.

func getGasPrices() -> (Double,Double,Double)    {        return (3.97,3.59,3.79)    }getGasPrices()

I don't know how to use the above method to receive the returned value.

The func parameters are also variable. You can put multiple parameters in an array.

func sumOf(sumbers:Int...) -> Int    {        var sum = 0        for number in sumbers        {            sum += number        }        return sum    }println(sumOf())    //return 0println(sumOf(42, 597, 12))   //return 651

Functions can be nested. nested functions can access variables declared in external functions. You can use nested functions to solve complicated logic:

    func returnFifteen() -> Int    {        var y = 10        func add()        {            y += 5        }        add()        return y;    }        println(returnFifteen()) //return 15

The function is of the first-class type, which means that the return value of the function can be another function:

Func makeIncrementer ()-> (Int-> Int) {func addOne (number: Int)-> Int {return 1 + number} return addOne} var increment = makeIncrementer () increment (7) // the above Code always reports an error, do not know what the cause // error: Command/Applications/Xcode6-Beta.app/Contents/Developer/Toolchains/XcodeDefault. xctoolchain/usr/bin/swift failed with exit code 254 // If any expert knows, please advise

A function can be used as another function as its parameter.

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,] let temp = hasAnyMatches (numbers, lessThanTen) println (temp) // This is the same as the above error, and I have a problem with xcode6.

You can use {} to create a closure.

numbers.map({    (number: Int) -> Int in    let result = 3 * number    return result    })

This closure can be written more concisely sometimes, for example, you know its return type or other

numbers.map({ number in 3 * number })

sort([1, 5, 3, 12, 2]) { $0 > $1 }

The closure above is not clear...