Benx Shen's Public Library

  class Strawberry
     def Strawberry.color
       return "red"
     end

     def self.size
       return "kinda small"
     end

     class << self
       def shape
         return "strawberry-ish"
       end
     end
   end
   Strawberry.color # -> "red"
   Strawberry.size  # -> "kinda small"
   Strawberry.shape # -> "strawberry-ish"

Note the three different constructions: ClassName.method_name and self.method_name are essentially the same - outside of a method definition in a class block, self refers to the class itself. The latter is preferred, as it makes changing the name of the class much easier. The last construction, class << self, puts us in the context of the class's "meta-class" (sometimes called the "eigenclass")

h = {"hash?" => "yep, it's a hash!", "the answer to everything" => 42, :linux => "fun for coders."}
puts "Stringy string McString!".class
puts 1.class
puts nil.class
puts h.class
puts :symbol.class

See? Everything is an object.

If I kept doing this, array2 wouldn't hold any elements. I can check for this condition by calling the empty? method. For example, the following bit of code moves all the elements from one array to another:

array1 << array2.pop until array2.empty?

Functions interact with blocks through the yield. Every time the function invokes yield control passes to the block. It only comes back to the function when the block finishes. Here's a simple example:

# Script block2.rb

def simpleFunction
  yield 
  yield
end

simpleFunction { puts "Hello!" }

$ block2.rb
Hello!
Hello!

In Ruby, methods that end with an exclamation mark (also called a "bang") modify the object. For example, the method upcase! changes the letters of a String to uppercase.

>> comedian.upcase!
=> "STEPHEN COLBERT"

Since both of the variables comedian and favorite_comedian point to the same String object, we can see the new, uppercase text using either variable.

>> comedian
=> "STEPHEN COLBERT"
>> favorite_comedian
=> "STEPHEN COLBERT"

in Ruby, there's a better way. You can use the %q operator to apply single-quoting rules, but choose your own delimiter to mark the beginning and end of the string literal.

puts %q!c:\napolean's documents\tomorrow's bus schedule.txt!
puts %q/c:\napolean's documents\tomorrow's bus schedule.txt/
puts %q^c:\napolean's documents\tomorrow's bus schedule.txt^
puts %q(c:\napolean's documents\tomorrow's bus schedule.txt)
puts %q{c:\napolean's documents\tomorrow's bus schedule.txt}
puts %q<c:\napolean's documents\tomorrow's bus schedule.txt>

The shebang line is read by the shell to determine what program to use to run the script. This line cannot be preceded by any blank lines or any leading spaces. The new hello-world.rb program – with the shebang line – looks like this:

#!/usr/bin/ruby

puts 'Hello world'