chapter twenty

Lesson 20 High 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

In Scala functions are first class citizens: you can use them as parameters or return them as the result of some computation. “High 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 code duplication and increase the reusability of your programs. In the capstone, you’ll use high 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: in the first one, you should display the result of your computation into the console, while in the second you should append it to an existing file. How would you design your functions to avoid code duplication and make sure 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