bench.rb

require "benchmark"

src = "[[tag, time, record['code'].to_i]]"
map = "#{src}"

tag = "foo"
time = 12345
record = {
  "code" => "400"
}

class A
end

a = A.new
a.singleton_class.module_eval(<<-CODE)
  def map_func(tag, time, record)
    #{map}
  end
CODE
a.singleton_class.class_eval <<-EORUBY, __FILE__, __LINE__ + 1
  def map_class_eval(tag, time, record)
    #{map}
  end
EORUBY

p a.map_class_eval(tag, time, record)
p a.map_func(tag, time, record)
p eval(src)
N = 10000
Benchmark.bmbm do |x|
  x.report("class_eval") do
    N.times do
      a.map_class_eval(tag, time, record)
    end
  end
  x.report("module_eval") do
    N.times do
      a.map_func(tag, time, record)
    end
  end
  x.report("eval") do
    N.times do
      eval(src)
    end
  end
end

result.log

$ ruby bench.rb 
[["foo", 12345, 400]]
[["foo", 12345, 400]]
[["foo", 12345, 400]]
Rehearsal -----------------------------------------------
class_eval    0.010000   0.000000   0.010000 (  0.005329)
module_eval   0.000000   0.000000   0.000000 (  0.003275)
eval          0.120000   0.000000   0.120000 (  0.120336)
-------------------------------------- total: 0.130000sec

                  user     system      total        real
class_eval    0.000000   0.000000   0.000000 (  0.003177)
module_eval   0.010000   0.000000   0.010000 (  0.003216)
eval          0.110000   0.000000   0.110000 (  0.118929)