Swift Programming: The Big Nerd Ranch Guide, 3rd Edition

Functions as Arguments

You initially sorted your volunteerCounts array using a named function passed as an argument to sorted(by:). Although that particular task could be accomplished elegantly without the need for a named function, there are times when declaring a function and passing it as an argument to another function is the best solution.

Now you will write your own function that takes a closure to modify a collection. In the playground, add this incomplete function:

Example 13.7. Formatting numbers as strings

...
func format(numbers: [Double], using formatter: (Double) -> String) -> [String] {
    var result = [String]()

    return result
}

That is a lot of parentheses! Do not be intimidated. Study the function’s signature from beginning to ...