method_definition.rb

require 'benchmark'

class TheHost
  define_method(:by_define_method) do
    24*4
  end

  def by_explicit_definition
    24*4
  end

  class_eval <<-EVAL
    def by_class_eval
      24*4
    end
  EVAL

  class_eval do
    def by_class_eval_block
      24*4
    end
  end

  module_eval <<-EVAL
    def by_module_eval
      24*4
    end
  EVAL
end

@@host = TheHost.new
TIMES = 1_000_000

Benchmark.bmbm do |x|
  %w( by_define_method by_explicit_definition by_class_eval by_class_eval_block by_module_eval ).each do |meth|
    x.report(meth) do
      TIMES.times do
        @@host.send(meth)
      end
    end
  end
end

results.rb

                             user     system      total        real
by_define_method         1.760000   0.400000   2.160000 (  2.158289)
by_explicit_definition   1.160000   0.240000   1.400000 (  1.391353)
by_class_eval            1.100000   0.260000   1.360000 (  1.370616)
by_class_eval_block      1.140000   0.240000   1.380000 (  1.394569)
by_module_eval           1.150000   0.260000   1.410000 (  1.429104)