class Regexp
  def Regexp.is_valid?(str)
    begin
      compile(str)
      valid = true
    rescue RegexpError
      valid = false
    end
  end
end
Regexp.is_valid? "The horror!"

Regexp.is_valid? "The)horror!"

def Fixnum.random(min, max)
  raise ArgumentError, "min > max" if min > max
  return min + rand(max-min+1)
end
Fixnum.random(10, 20)

Fixnum.random(-5, 0)

Fixnum.random(10, 10)

Fixnum.random(20, 10)                             

ArgumentError: min > max
...

ArgumentError: min > max
	from (irb):14:in `random'
	from (irb):20

company_name = 'Homegrown Software'
def company_name.legalese
  return "#{self} is a registered trademark of ConglomCo International."
end
company_name.legalese

'Some Other Company'.legalese

NoMethodError: undefined method `legalese' for "Some Other Company":String
...

NoMethodError: undefined method `legalese' for "Some Other Company":String
	from (irb):26

class Button
  #A stub method to be overridden by subclasses or individual Button objects
  def pushed
  end
end
buttonA = Button.new
def buttonA.pushed
  puts "You pushed me! I'm offended!"
end
buttonB = Button.new
def buttonB.pushed
  puts "You pushed me; that's okay."
end
Button.new.pushed
#
buttonA.pushed

You pushed me! I'm offended!

You pushed me! I'm offended!

buttonB.pushed

You pushed me; that's okay.

You pushed me; that's okay.