Using a single object vs. creating a new one each time. Pretty basic Ruby stuff but I still see this anti-pattern all over the place.

ruby_object_test.rb

class ClassThatDoesStuff

  def some_method
    "You're winner!"
  end

end

require 'benchmark'

puts "Using a single instance : 5000 times"
Benchmark.benchmark do |x|
  x.report do 
    doer = ClassThatDoesStuff.new
    5000.times{|n| doer.some_method}
  end
end

puts "\n"
puts "Creating an instance each time : 5000 times"
Benchmark.benchmark do |x|
  x.report do 
    5000.times{|n| ClassThatDoesStuff.new.some_method}
  end
end

puts "\n\n"

jon:~/src/candy (ruby-1.9.3-p484)
 $ ruby ruby_object_test.rb
Using a single instance : 5000 times
    0.000000   0.000000   0.000000 (  0.000540)

Creating an instance each time : 5000 times
    0.000000   0.000000   0.000000 (  0.001040)