compose function in swift

In Swift, functions can be composed just like any other data type. Function composition is the act of chaining multiple functions together, where the output of one function is passed as the input to the next.

We can compose functions using either the compose or >>> operator. The compose operator takes two functions and returns a new function, which when called with an argument, applies the second function to the result of the first function. The >>> operator is similar, but reads left to right.

Here's an example using the compose operator:

main.swift
func addOne(_ x: Int) -> Int {
    return x + 1
}

func multiplyByTwo(_ x: Int) -> Int {
    return x * 2
}

let composed = compose(multiplyByTwo, addOne)
let result = composed(3) // result is 8
195 chars
11 lines

Here's the same example using the >>> operator:

main.swift
let composed = multiplyByTwo >>> addOne
let result = composed(3) // result is 8
80 chars
3 lines

This is made possible by the fact that functions are first-class citizens in Swift, which means that they can be used just like any other value or expression. We can pass them as arguments to other functions, return them from functions, and store them in variables or data structures. These features allow us to use higher-order functions and closures to make our code more expressive and modular.