From: Gavin Kistner <gavin@...>
Date: 2005-05-17T22:45:59+09:00
Subject: Re: Extending an Instance only Once

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On May 17, 2005, at 7:01 AM, Peter wrote:
>> I have a method that requires that the arguments passed to it have  
>> been in-mixed with a module. Currently, my code looks like this:
>>
>> def my_method( the_obj )
>>    the_obj.extend( MyModule ) unless the_obj.inherits_from? 
>> ( MyModule )
>> end
> This does not proof the check is actually done, but in the source  
> you can see that check is actually there without doubt.
>
> The same goes for Object#extend because it is implemented as an  
> include in the singleton class (or selfclass as some people  
> prefer :) which obeys the same rules as includes in regular  
> classes. So no need to check this yourself!

Hrm...I see code that looks like that's what's going on inside of  
class.c, but apparently it is faster to test myself:


require 'benchmark'
include Benchmark

module M; end
class Bar < Array; end
class Foo < Bar; end

n = 500000
bm(15){ |x|
     f = Foo.new
     x.report( "Always Extend" ){
         n.times{
             x.extend( M )
         }
     }

     f = Foo.new
     x.report( "Test First" ){
         n.times{
             x.extend( M ) unless x.is_a?( M )
         }
     }
}

                      user     system      total        real
Always Extend    1.610000   0.010000   1.620000 (  1.983911)
Test First       0.730000   0.000000   0.730000 (  0.745857)


Is there a flaw with my test above?

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