Higher-Order Functions
Higher-order functions are functions that can take another function as an argument or can return a function.
You have already worked with higher-order functions in this chapter and even written your own, like format(numbers:using:).
Let’s take a look at three higher-order functions from the standard library – map(_:), filter(_:), and reduce(_:_:) – in the context of your imaginary volunteerism reports.
map(_:)
The Swift standard library provides an implementation of map(_:) as a method on the Array type.
It is used to transform an array’s contents.
You map an array’s contents from one value to another and put the new values into a new array.
Because map(_:) is a higher-order function, you provide it with another ...
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