Ruby attr_accessor与getter/setter基准测试:为什么accessor更快?

我刚刚针对等效的getter/setter方法测试了attr_accessor:

I just tested attr_accessor against equivalent getter/setter-methods:

class A
  # we define two R/W attributes with accessors
  attr_accessor :acc, :bcc

  # we define two attributes with getter/setter-functions
  def dirA=(d); @dirA=d; end
  def dirA; @dirA; end
  def dirB=(d); @dirB=d; end
  def dirB; @dirB; end
end

varA   = A.new
startT = 0
dirT   = 0
accT   = 0

# now we do 100 times the same benchmarking
# where we do the same assignment operation
# 50000 times
100.times do
  startT = Time.now.to_f
  50000.times do |i|
    varA.dirA = i
    varA.dirB = varA.dirA
  end
  dirT += (Time.now.to_f - startT)

  startT = Time.now.to_f
  50000.times do |i|
    varA.acc = i
    varA.bcc = varA.acc
  end
  accT += (Time.now.to_f - startT)
end

puts "direct:   %10.4fs" % (dirT/100)
puts "accessor: %10.4fs" % (accT/100)

程序输出为:

direct:       0.2640s
accessor:     0.1927s

因此，attr_accessor明显更快.有人可以分享一些智慧吗，为什么会这样呢?

So the attr_accessor is significantly faster. could someone please share some wisdom, why this is so?