Wintermeyer - Learn Rails 5.2: Accelerated Web Development with Ruby on Rails

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Stefan Wintermeyer 2018

Stefan Wintermeyer Learn Rails 5.2

1. Ruby Introduction

Stefan Wintermeyer 1

(1)

Bochum, Germany

This chapter is a tightrope walk between oversimplification and a degree of detail that is unnecessary for a Rails newbie. After all, the objective is not to become a Ruby guru but to understand Ruby on Rails. I will elaborate on the most important points, and the rest is then up to you. If you would like to know more about Ruby, I recommend the book The Ruby Programming Language by David Flanagan and Yukihiro Matsumoto.

It is easy to program in Ruby, but Ruby is not a simple language.

Yukihiro Matsumoto

Ruby 2.5

Im going to use Ruby 2.5, but for most part of this book you can use older versions too. Ruby 2.5 is just a bit faster. You can check the installed Ruby version by running the command ruby -v , as shown here:

$ ruby -v

ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-darwin17]

$

If your system is running an older version and you want to upgrade it, take a look at https://rvm.io , which is my preferred way of installing and using different Ruby versions.

Basics

Ruby is a scripting language. So, it is not compiled and then executed; instead, it is read by an interpreter and then processed line by line.

Hello World

A simple hello-world.rb program consists of one line of code, as shown in Listing .

puts 'Hello World!'

Listing 1-1

hello-world.rb

Use your favorite editor to open a new file with the filename hello-world.rb and insert the previous line into it. You can then execute this Ruby program at the command line as follows:

$ ruby hello-world.rb

Hello World!

$

A program line in a Ruby program does not have to end with a semicolon. The Ruby interpreter is even so intelligent that it recognizes if a program line was split over two or more lines for the sake of readability. Indenting code is also not necessary. But it does make it much easier to read for human beings!

puts and print

If you look for examples on Ruby on the Internet, you will find two typical ways of printing text on the screen.

• puts prints a string, followed by a newline.
• print prints a string (without a newline).

Listing shows an example program (an extension of the program hello-world.rb ).

puts 'Hello World!'

puts

puts 'zzz'

print 'Hello World!'

print

puts 'zzz'

Listing 1-2

hello-world.rb

On the screen, you will see this:

$ ruby hello-world. rb

Hello World!

zzz

Hello World!zzz

Comments

A comment in a Ruby program starts with a # sign and ends with a newline. As an example, I added a comment to the earlier hello-world.rb program; see Listing .

# Program for displaying "Hello World!"

# by Stefan Wintermeyer

puts 'Hello World!'

Listing 1-3

hello-world.rb

A comment can also follow a program line, as shown in Listing .

puts 'Hello World!' # Example comment

Listing 1-4

hello-world.rb

A # sign within strings in a single quote mark is not treated as the start of a comment, as shown in Listing .

# Example program

# by Stefan Wintermeyer

puts 'Hello World!'

puts '############'

puts

puts '1#2#3#4#5#6#' # Comment on this

Listing 1-5

hello-world.rb

Help via ri

When programming , you do not always have a Ruby handbook available. Fortunately, the Ruby developers thought of this and provided a built-in help feature in form of the program ri .

Of course, you must have installed the documentation, which is the default. If you used rvm to install Ruby, you can run rvm docs generate to generate the documentation.

This is a typical chicken-and-egg situation. How can I explain the Ruby help feature if you are only just getting started with Ruby? So, I am going to jump ahead a little and show you how you can search for information on the class String .

$ ri String

[...]

$

Many times it is easier and more informative to use Google instead of ri .

irb

irb stands for I nteractive R u b y and is a kind of sandbox where you can play around with Ruby at your leisure. You can launch irb by entering irb on the shell and end it by entering exit .

An example is worth a thousand words.

$ irb

irb(main):001:0> puts 'Hello World!'

Hello World!

=> nil

irb(main):002:0> exit

$

In future examples, I use IRB.conf[:PROMPT_MODE] = :SIMPLE in my .irbrc config file to generate shorter irb output (without the irb(main):001:0> part). You can do the same by using irb --simple-prompt .

Ruby Is Object-Oriented

Ruby only knows objects. Everything is an object (sounds almost like Zen). Every object is an instance of a class. You can find out the class of an object via the method .class .

An object in Ruby is encapsulated and can be reached from the outside only via the methods of the corresponding object. What does this mean? You cannot change any property of an object directly from the outside. The corresponding object has to offer a method with which you can do so.

Please do not panic if you have no idea what a class or an object is. I wont tell anyone, and you can still work with them just fine without worrying too much. This topic alone could fill whole volumes. Roughly speaking, an object is a container for something, and a method changes something in that container.

Please go on reading and take a look at the examples. The puzzle will gradually get clearer.

Methods

In other programming languages , the terms you would use for Ruby methods would be functions , procedures , subroutines , and of course methods .

Here I go with the oversimplification. You cannot compare non-object-oriented programming languages with object-oriented ones. Plus, there are two kinds of methods (class methods and instance methods). I do not want to make it too complicated. So, I simply ignore those fine distinctions.

At this point, you probably want to look at a good example, but all I can think of are silly ones. The problem is the assumption that you are only allowed to use knowledge that has already been described in this book .

So, lets assume that you use the code sequence in Listing repeatedly (for whatever reason).

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