The Ruby Programming Language

A Tour of Ruby

This section is a guided, but meandering, tour through some of the most interesting features of Ruby. Everything discussed here will be documented in detail later in the book, but this first look will give you the flavor of the language.

Ruby Is Object-Oriented

We’ll begin with the fact that Ruby is a completely object-oriented language. Every value is an object, even simple numeric literals and the values true, false, and nil (nil is a special value that indicates the absence of value; it is Ruby’s version of null). Here we invoke a method named class on these values. Comments begin with # in Ruby, and the => arrows in the comments indicate the value returned by the commented code (this is a convention used throughout this book):

1.class      # => Fixnum: the number 1 is a Fixnum
0.0.class    # => Float: floating-point numbers have class Float
true.class   # => TrueClass: true is a the singleton instance of TrueClass
false.class  # => FalseClass
nil.class    # => NilClass

In many languages, function and method invocations require parentheses, but there are no parentheses in any of the code above. In Ruby, parentheses are usually optional and they are commonly omitted, especially when the method being invoked takes no arguments. The fact that the parentheses are omitted in the method invocations here makes them look like references to named fields or named variables of the object. This is intentional, but the fact is, Ruby is very strict about encapsulation of its objects; there is ...