Swift Functional Programming - Second Edition

Function types

Along with, classes, structs, enums, and protocols, functions can also be used as types in Swift. In this section, we will explore how we can define functions as types and how we can use function types. Let's first discover what the type of the function is and how it is defined.

A function parameter type along with its return type defines the type of the function. For instance, the function type for the following coding example is (Int, Double) -> String:

func functionName(firstParam: Int, secondParam: Double) -> String 

We will be able to use function types in the way we use other types. The following code example presents a function type:

var simpleMathOperator: (Double, Double) -> Double 

Here, simpleMathOperator is a ...