From: Albert Schlef <albertschlef@...>
Date: 2010-02-05T06:42:59+09:00
Subject: Re: Where is the magic?

Ilya Lopatkin wrote:
> Robert Klemme wrote:
>> Struct.new uses instance_eval internally:
>> 
> 
> Thanks for your response. I've almost grasped the idea. :)

Here's an explanation is other words:

When you create a block you create a parcel that contains three things:

  - The code itself.
  - The "binding" (links to the surrounding variables).
  - The value of 'self' (this is how ruby knows which object to
    invoke methods on).

When you normally 'yield' to a block, the block uses the value of 'self' 
saved in that parcel. On the other hand, when you do 
'somebody.eval_instance()', the 'self' in that parcel is set to 
'somebody'.

It is common in GUI frameworks to use eval_instance() to make the code 
look like DSL (google for "DSL").
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