20 Higher Order Functions

 

After reading this lesson, you will be able to:

  • Define functions that have functions as parameters
  • Implement functions that return functions
  • Build powerful abstractions that remove code duplication

Functions are first-class citizens in Scala: you can use them as parameters or return them as the result of some computation. “Higher order functions” are functions that accept other functions as parameters, or that return functions, or both. Their use allows you to create powerful abstractions that reduce duplication and increase the reusability of your code. In the capstone, you’ll use higher order functions to extract information on the winner of the game “Paper, Rock, Scissors, Lizard, Spock!”.

Consider this

Suppose you want to compute some calculations and perform some input/output operation on them. For example, you may need to express two case scenarios: you should display the result of your computation into the console in the first, while you should append it to an existing file in the second. How would you design your functions to avoid code duplication and ensure their implementation is consistent everywhere in your program? How efficiently can you add support for other IO operations, such as querying a database?

20.1  Functions as Parameters

20.2  Functions as return values

20.3  Summary

20.4  Answers to Quick Checks