require 'benchmark'

class Symbol
  def to_proc
    Proc.new { |*args| args.shift.__send__(self, *args) }
  end
end

n = 10000

s = Struct.new :id
messages = []
n.times { messages << s.new(:id => rand(n)) }

Benchmark.bm do |x|  
  # Integer
  x.report { n.times { messages.map{|m| m.id} } }
  x.report { n.times { messages.map(&:id) } }
end

# $ ruby perform.rb 
#       user     system      total        real
#  33.280000   0.860000  34.140000 ( 34.912584)
# 191.940000   1.660000 193.600000 (197.168849)