Variable And Function Calls On Lines By Themselves In Swift

Question

I'm reading the iBook The Swift Programming Language and seeing a convention that I don't understand and hasn't been explained in the book: variable and functions followed by a single line with the variable or function name by itself.

For example:

var n = 2
while n < 100 {
    n = n * 2
}
n

var m = 2
do {
    m = m * 2
} while m < 100
m

And:

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

What is the purpose of these lines where the variable or function name are on a line by themselves?

TIA

Answer 1

The purpose is for "Playground" Demonstrations. For example, if you put that code into playground. The window on the right will show result of the execution of the function.

If you were in a traditional project, you would likely do:

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

However, this is unnecessary in Playground:

Notice the right side.

Answer 2

When you are using Swift in the playground, the output display on the right hand side is not actually a console output more so just an output of whatever variable is on that line, or the number of times a loop runs.

So they are placing the variable/function on it's own line so that when you paste that into Playground you will see what the result is.