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PODelegator through BasicObject transparency
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copied!<p><strong>Context</strong>: I am trying to put up a Decorator pattern in Ruby. As a Decorator should delegate all unknown methods to the underlying objects, I used the Delegator class. I could have used SimpleDelegator but I wanted to fully understand what I was doing.</p> <p>So the basic code I came out with was :</p> <pre><code>class Decorator < Delegator def initialize(component) super @component = component end def __setobj__(o); @component = o end def __getobj__; @component end def send(s, *a); __send__(s, *a) end end </code></pre> <p>Which is ~exactly the same as the implementation of SimpleDelegator. Seems good.</p> <p>But the thing I did not want was for the code handling the Decorator to know it is manipulating a Decorator. I want full transparency.</p> <p>At this moment <code>Decorator.new(Object.new).class</code> returned <code>Decorator</code></p> <p>So I tinkered a bit and came up with this :</p> <pre><code>class Decorator < Delegator undef_method :== undef_method :class undef_method :instance_of? # Stores the decorated object def initialize(component) super @component = component end def __setobj__(o); @component = o end def __getobj__; @component end def send(s, *a); __send__(s, *a) end end </code></pre> <p>This way, I can safely use <code>class</code> or <code>instance_of?</code> on my Decorated object, it will send the method to the underlying object via method_missing (which is implemented by Delegator).</p> <p>The thing is : I don't understand why I had to undef <code>:class</code> and <code>:instance_of?</code>. I can see that BasicObject defines <code>:==</code> so I had to undefine it but what about those two ? I looked at the BasicObject documentation and a bit in the C code but did not find anything. I looked the same at the Delegator documentation and code, and did not find anything either. It seems Delegator include the Kernel module, but Kernel#class or Kernel#instance_of? don't exist.</p> <p>Where those two method came from ? Why did I need to undefine them if they were not implemented at all ? I guess I must be missing something about Ruby's object model or something.</p> <p>Thanks.</p>

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