From: Dominik Bathon <dbatml@...>
Date: 2006-02-19T01:15:30+09:00
Subject: Re: define_method fun

On Sat, 18 Feb 2006 06:49:37 +0100, Joel VanderWerf  
<vjoel@path.berkeley.edu> wrote:

> Patrick Ritchie wrote:
>> Hi All,
>>
>> I just setup the following in one of my classes, I'll let the code speak
>> for itself:
>>
>> ["<", "<=", ">", ">=", "==", "<=>"].each do |op|
>>  define_method(op) { |comparison| eval "#{self.order} #{op}
>> #{comparison.order}" }
>> end
>>
>> Ruby continues to impress me with it's ability to do so much in so few
>> amazing readable lines of code.
>>
>> Are their any good reasons not to declare my op methods this way? Is
>> their an even more efficient way to achieve the same effect?
>
> It helps to pull the eval out of the define_method:

Or using no eval at all:

> module Order
>   attr_reader :order
>   def initialize order
>     @order = order
>   end
> end
>
> class EvalInside
>   include Order
>   ["<", "<=", ">", ">=", "==", "<=>"].each do |op|
>     define_method(op) { |comparison| eval "#{self.order} #{op}
> #{comparison.order}" }
>   end
> end
>
> class EvalOutside
>   include Order
>   ["<", "<=", ">", ">=", "==", "<=>"].each do |op|
>     eval "define_method(:#{op}) { |comparison| self.order #{op}
> comparison.order }"
>   end
> end

class NoEval
   include Order
   [:<, :<=, :>, :>=, :==, :<=>].each do |op|
     define_method(op) { |comparison| self.order.send(op, comparison.order)  
}
   end
end

> require 'benchmark'
>
> inside = []
> outside = []
noeval = []
400000.times do |i|
>   order = rand(1)
>   inside << EvalInside.new(i)
>   outside << EvalOutside.new(i)
   noeval << NoEval.new(i)
> end
>
> Benchmark.bmbm do |bm|
>   bm.report("eval inside") do
>     inside.sort
>   end
>
>   bm.report("eval outside") do
>     outside.sort
>   end

   bm.report("no eval") do
     noeval.sort
   end
> end

Rehearsal ------------------------------------------------
eval inside   19.310000   0.060000  19.370000 ( 19.500018)
eval outside   1.940000   0.010000   1.950000 (  1.951829)
no eval        2.600000   0.010000   2.610000 (  2.626695)
-------------------------------------- total: 23.930000sec

                    user     system      total        real
eval inside   18.690000   0.080000  18.770000 ( 18.950481)
eval outside   1.920000   0.000000   1.920000 (  1.940485)
no eval        2.010000   0.000000   2.010000 (  2.028688)


Dominik