From: Drew Olson <olsonas@...>
Date: 2008-03-08T06:21:02+09:00
Subject: Re: instance_eval and class_eval - names got mixed up?

Bharat Ruparel wrote:
> Thanks gentlemen for your responses.  It still requires mental gyrations 
> for me.  I honestly think that this one got away from Matz.

The confusion here is that you're calling instance eval on a specific 
class. In ruby, classes are instances of the Class class (no, that is 
not a type). Methods added to your class (the instance of the class 
Class) are, in effect, added the the class definition. Below is an 
example of using class_eval and instance_eval against a simple class, so 
you might find this less confusing.

>> class Foo
>>   def hi
>>     puts "hi"
>>   end
>> end
=> nil
>> foo = Foo.new
=> #<Foo:0x3aa250>
>> foo.instance_eval do
?>   hi
>> end
hi
=> nil
>> Foo.class_eval do
?>   def howdy
>>     puts "howdy"
>>   end
>> end
=> nil
>> foo.howdy
howdy
=> nil
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