Mastering Ruby Closures: A Guide to Blocks, Procs, and Lambdas

92 Pages·2017·2.228 MB·English

by  Benjamin Tan Wei Hao

Early Praise for Mastering Ruby Closures
This is an excellent book for experienced Ruby developers to add functional pro-
gramming paradigms to their toolkit. This book gives excellent examples of blocks,
Procs, and lambdas and ways to use them in your existing application.
➤ Jeffrey Holland
Senior software engineer, Ackmann & Dickenson
I’ve been a Rubyist for over a decade, and I still learned several new techniques
and how to avoid gotchas with Procs, lambdas, and blocks. This book is also perfect
for the Ruby/Rails developer who wants to feel confident when consuming or
writing libraries that use Ruby’s closures. Easy to understand, interesting exam-
ples, and a solid reference.
➤ Matthew Margolis
Director, software engineering, Getty Images
You’ve probably called methods that take in a block, but if you’ve not written a
method that takes in a block, I highly recommend this book to you. Once you’re
through with the book, you’ll be able to explain how [1,2,3].map(&:to_s) works with
confidence. I’ve always been a fan of Benjamin’s writing because every concept is
always followed up by real-world examples, which makes it easier for the reader
to grok the concepts being taught.
➤ Tan Guo Xiang
Software engineer, Civilized Discourse Construction Kit
I never heard Ruby could do closures, but Mastering Ruby Closures brought me
from zero to hero in just a few hours! Don’t be afraid, and take a look yourself!
➤ Gábor László Hajba
Software engineer, Zühlke Engineering
Mastering Ruby Closures
A Guide to Blocks, Procs, and Lambdas
Benjamin Tan Wei Hao
The Pragmatic Bookshelf
Raleigh, North Carolina
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Printed in the United States of America.
ISBN-13: 978-1-68050-261-9
Encoded using the finest acid-free high-entropy binary digits.
Book version: P1.0—August 2017
To my parents, Virginia and Michael,
and to my favorite girls in the world,
Hui Ling and Gu Gu.

Contents
Acknowledgements . . . . . . . . . . . ix
Welcome! . . . . . . . . . . . . . xi
1. Closing in on Closures . . . . . . . . . . 1
The Foundations of a Closure 1
Simulating Classes with Closures 5
Implementing Callbacks in Ruby with Lambdas 7
Implementing Enumerable#reduce() (or Fold Left) 11
Test Your Understanding! 15
Wrapping Up 16
2. Beautiful Blocks . . . . . . . . . . . . 17
Separating the General from the Specific 18
Executing Blocks with the yield Keyword 19
Blocks as Closures and Block Local Variables 21
Block Pattern #1: Enumeration 22
Block Pattern #2: Managing Resources 26
Block Pattern #3: Beautiful Object Initialization 29
Test Your Understanding! 37
Wrapping Up 39
3. The Power of Procs and Lambdas . . . . . . . 41
Procs and the Four Ways of Calling Them 42
Lambdas—Same, But Different 44
How Symbol#to_proc Works 47
Currying with Procs 52
Test Your Understanding! 55
Wrapping Up 56
4. Building Your Own Lazy Enumerables . . . . . . 57
Understanding Lazy Enumerables 57
Contents • viii
Building Our Skeleton 59
Implementing Lax 63
Implementing Lazy map() 66
Implementing Lazy take() 67
Test Your Understanding! 69
Wrapping Up 70
A1. Solutions . . . . . . . . . . . . . 71
Chapter 1 71
Chapter 2 72
Chapter 3 74
Chapter 4 74
Bibliography . . . . . . . . . . . . . 77