interesting error catching method / singleton_class (class << self) stuff

test_errors.rb

def errors_with_message(pattern)
  # Generate an anonymous "matcher module" with a custom threequals m = Module.new
  m = Module.new
# next 3 lines are equivalent
#  (m.singleton_class.class_eval { self }).instance_eval do
  m.singleton_class.instance_eval do
#  (class << m; self; end).instance_eval do
    define_method(:===) do |e|
      pattern === e.message
    end 
  end
  m
end

begin
  raise 'blaherror'
rescue errors_with_message(/blah/)
  puts "caught blah error"
end