Ruby Open Classes - Code Examples

1-email-validator.rb

class String
  # taken from: http://regexlib.com/REDetails.aspx?regexp_id=2558 - (escaped the forward-slashes as well)  
  def is_email?
    self =~ /^((([!#$\%&'*+\-\/=?^_`{|}~\w])|([!#$\%&'*+\-\/=?^_`{|}~\w][!#$\%&'*+\-\/=?^_`{|}~\.\w]{0,}[!#$\%&'*+\-\/=?^_`{|}~\w]))[@]\w+([-.]\w+)*\.\w+([-.]\w+)*)$/
  end
  
  def isnt_email?
    !is_email?
  end
end

puts "See this is an email!" if "[email protected]".is_email?
puts "And so is this" if "[email protected]".is_email?
puts "but I'm not!" if "fail".isnt_email?

2-error-messages.rb

# pretend this is in an OSS library..
class PrinterError
  attr_reader :code
  
  def initialize(code)
    @code = code
  end
end

# So at this point the code is defined elsewhere, let's open it up to add our messages.

class PrinterError
  def message
    @code == 42 ? "PC LOAD ERROR" : "Unexpected error printing document"
  end
end

puts PrinterError.new(100).message
puts PrinterError.new(42).message

3-dark-side.rb

# using a completey normal string method..

puts "oh hai!".upcase

# along comes a naughty developer

class String
  def upcase
    "#{self}\nCATS: ALL YOUR BASE ARE BELONG TO US."
  end
end
  
# now what happens when we call the same code as before??

puts "oh hai!".upcase

README.md

From blog post here.