output

[james@kremlin00 ruby (klasscache)]$./ruby  -I . -I lib ./test.rb 
method cache invalidations: 18
A
B
method cache invalidations: 18

test.rb

class A
  def a
    puts 'A'
  end
end

module B
  def a
    puts 'B'
  end
end

puts "method cache invalidations: #{RubyVM::MethodCache.invalidations}"

A.new.a
class A
  def a
    puts 'B'
  end
end
A.new.a

puts "method cache invalidations: #{RubyVM::MethodCache.invalidations}"