Ruby is sexy, Ruby is cool and its metaprogramming potential offers some really cook features. However you might not realize that your cleverness is slowing down your code.
Today I was working on cleaning up merb_helper a Merb plugin that brings a lot of the stuff Rails developers are used to. In Merb we aim for speed and try to avoid magic.
merb_plugin didn’t receive a lot of love from the main contributors but few features were added by different contributors and the code became hard to maintain.
Looking at the code I quickly found this bad boy:
(Old Merb Time DSL using metaprogramming)
module MetaTimeDSL
{:second => 1,
:minute => 60,
:hour => 3600,
:day => [24,:hours],
:week => [7,:days],
:month => [30,:days],
:year => [364.25, :days]}.each do |meth, amount|
define_method "m_#{meth}" do
amount = amount.is_a?(Array) ? amount[0].send(amount[1]) : amount
self * amount
end
alias_method "m_#{meth}s".intern, "m_#{meth}"
end
end
Numeric.send :include, MetaTimeDSL
The above code looks awful to me and I decided to rewrite it a way I thought would be more efficient:
module TimeDSL
def second
self * 1
end
alias_method :seconds, :second
def minute
self * 60
end
alias_method :minutes, :minute
def hour
self * 3600
end
alias_method :hours, :hour
def day
self * 86400
end
alias_method :days, :day
def week
self * 604800
end
alias_method :weeks, :week
def month
self * 2592000
end
alias_method :months, :month
def year
self * 31471200
end
alias_method :years, :year
end
Numeric.send :include, TimeDSL
To make sure I was right, I run the following benchmarks:
require 'benchmark'
TIMES = (ARGV[0] || 100_000).to_i
Benchmark.bmbm do |x|
x.report("metaprogramming 360.seconds") do
TIMES.times do
360.m_seconds
end
end
x.report("no metaprogramming 360.hours") do
TIMES.times do
360.seconds
end
end
x.report("metaprogramming 360.minutes") do
TIMES.times do
360.m_minutes
end
end
x.report("no metaprogramming 360.minutes") do
TIMES.times do
360.minutes
end
end
x.report("metaprogramming 360.hours") do
TIMES.times do
360.m_hours
end
end
x.report("no metaprogramming 360.hours") do
TIMES.times do
360.hours
end
end
x.report("metaprogramming 360.days") do
TIMES.times do
360.m_days
end
end
x.report("no metaprogramming 360.days") do
TIMES.times do
360.days
end
end
x.report("metaprogramming 360.weeks") do
TIMES.times do
360.m_weeks
end
end
x.report("no metaprogramming 360.weeks") do
TIMES.times do
360.weeks
end
end
x.report("metaprogramming 18.months") do
TIMES.times do
18.m_months
end
end
x.report("no metaprogramming 18.months") do
TIMES.times do
18.months
end
end
x.report("metaprogramming 7.years") do
TIMES.times do
7.m_years
end
end
x.report("no metaprogramming 7.years") do
TIMES.times do
7.years
end
end
end
Rehearsal ------------------------------------------------------------------
metaprogramming 360.seconds 0.130000 0.000000 0.130000 ( 0.133164)
no metaprogramming 360.hours 0.050000 0.000000 0.050000 ( 0.042655)
metaprogramming 360.minutes 0.130000 0.000000 0.130000 ( 0.133327)
no metaprogramming 360.minutes 0.040000 0.000000 0.040000 ( 0.042401)
metaprogramming 360.hours 0.140000 0.000000 0.140000 ( 0.134312)
no metaprogramming 360.hours 0.040000 0.000000 0.040000 ( 0.043125)
metaprogramming 360.days 0.130000 0.000000 0.130000 ( 0.134949)
no metaprogramming 360.days 0.050000 0.000000 0.050000 ( 0.043745)
metaprogramming 360.weeks 0.130000 0.000000 0.130000 ( 0.135581)
no metaprogramming 360.weeks 0.050000 0.000000 0.050000 ( 0.043544)
metaprogramming 18.months 0.130000 0.000000 0.130000 ( 0.135234)
no metaprogramming 18.months 0.050000 0.000000 0.050000 ( 0.044354)
metaprogramming 7.years 0.140000 0.000000 0.140000 ( 0.144062)
no metaprogramming 7.years 0.050000 0.000000 0.050000 ( 0.044392)
--------------------------------------------------------- total: 1.260000sec
user system total real
metaprogramming 360.seconds 0.130000 0.000000 0.130000 ( 0.132567)
no metaprogramming 360.hours 0.040000 0.000000 0.040000 ( 0.042777)
metaprogramming 360.minutes 0.140000 0.000000 0.140000 ( 0.132554)
no metaprogramming 360.minutes 0.040000 0.000000 0.040000 ( 0.043193)
metaprogramming 360.hours 0.130000 0.000000 0.130000 ( 0.133027)
no metaprogramming 360.hours 0.050000 0.000000 0.050000 ( 0.042613)
metaprogramming 360.days 0.130000 0.000000 0.130000 ( 0.138637)
no metaprogramming 360.days 0.050000 0.000000 0.050000 ( 0.043213)
metaprogramming 360.weeks 0.130000 0.000000 0.130000 ( 0.134049)
no metaprogramming 360.weeks 0.040000 0.000000 0.040000 ( 0.043713)
metaprogramming 18.months 0.140000 0.000000 0.140000 ( 0.134941)
no metaprogramming 18.months 0.040000 0.000000 0.040000 ( 0.043980)
metaprogramming 7.years 0.150000 0.000000 0.150000 ( 0.143389)
no metaprogramming 7.years 0.040000 0.000000 0.040000 ( 0.044585)
0.136591)
The metaprogramming version of the same implementation is almost 3 times slower!
Moral of the story: be careful when using metaprogramming, you might end up slowing down your code considerably.
