[Newbie] The pickaxe book and benchmark

Rails
1

Hello,

I was reading the pickaxe book and then I arrived to the chapter

“When trouble strikes” in the Benchmark section.

I have this code:

#!/usr/bin/ruby -w
require ‘benchmark’
include Benchmark

LOOP_COUNT = 1_000_000

bm(12) do |test|
test.report(“normal:”) do
LOOP_COUNT.times do |x|
y = x +1
end
end
test.report(“predefine:”) do
x = y = 0
LOOP_COUNT.times do |x|
y = x + 1
end
end
end

The “predefine” test is more fast than the “normal”. Why?
The only difference that I see is x = y = 0 but I don’t understand

thanks!

                               Rafael G.
2

Rafa G. wrote:

LOOP_COUNT.times do |x|
  y = x + 1
end

end
end

The “predefine” test is more fast than the “normal”. Why?
The only difference that I see is x = y = 0 but I don’t understand

thanks!
Because of scope. In the second test, x and y are defined in the scope
outside the code block, and the block uses the outside variables. In the
first block, the variables are created for each iteration of the loop.

3

Thanks!