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Scala Functional Programming Patterns

You're reading from   Scala Functional Programming Patterns Grok and perform effective functional programming in Scala

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Product type Paperback
Published in Dec 2015
Publisher
ISBN-13 9781783985845
Length 298 pages
Edition 1st Edition
Languages
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Author (1):
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Atul S. Khot Atul S. Khot
Author Profile Icon Atul S. Khot
Atul S. Khot
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Table of Contents (13) Chapters Close

Preface 1. Grokking the Functional Way FREE CHAPTER 2. Singletons, Factories, and Builders 3. Recursion and Chasing your Own Tail 4. Lazy Sequences – Being Lazy, Being Good 5. Taming Multiple Inheritance with Traits 6. Currying Favors with Your Code 7. Of Visitors and Chains of Responsibilities 8. Traversals – Mapping/Filtering/Folding/Reducing 9. Higher Order Functions 10. Actors and Message Passing 11. It's a Paradigm Shift Index

Null Objects – singletons in another garb


One popular form in which singletons are used is the Null Object pattern. Let's see what a Null Object is.

Java gives us the null reference to indicate a missing value. We are not supposed to call a method on it as there is no object. If, erroneously, we do, we are greeted with a Null Pointer Exception (NPE). When we design methods to return nulls, the client code that calls the method needs to check assiduously. This is what a typical null check-based Java code looks like:

       Point p = makeAPoint(); // a method that returns null in some cases
       if (p != null) { // the dreaded null check – onus is on us...
            // We are on sure grounds
       }

The problem is that the onus term is on us to check for a reference being null. Every call to makeAPoint() needs to be checked, as shown earlier. This soon becomes tedious.

Note

The inventor of the null keyword called it his billion-dollar mistake!!! Please see http://www.infoq.com/presentations...

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