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    <p>If I absolutely do not want the Hash-like object to have certain hash methods, then I would wrap the object in my own class and only expose the methods I want it to have (your option b).</p> <p>If I wanted it to maintain its true hash behavior with some added behavior, I would add that behavior in a module to the hash object itself, not modifying the core hash class:</p> <pre><code>module SpecialHash def reindex # method def end end my_hash = {} my_hash.extend(SpecialHash) my_hash.reindex #now is defined on my hash </code></pre> <p>Most commonly, one of these options will do the trick for me.</p> <p>In general, I tend to favor using modules to extend class behavior instead of class inheritance because I consider it to be a cleaner and more lightweight approach. Creating a new class always gives me the feeling that I am adding a new "thing" to my domain model. This is fine and is exactly what you want to do in countless scenarios, but Ruby's mixin capabilities give you a very nice alternative when you don't actually need to go quite that far. </p> <p>The main time when I would deal with creating a class is if there is some additional state in the object that I want to keep track of. If my additions are not about expanding on the state of the object, but are just about expanding on it's behavior, then I will almost always start by mixing that behavior into an existing instance of that class using a module. </p> <p>Another answer to this sort of question also brings up some other points worth keeping in mind as well: <a href="https://stackoverflow.com/questions/1282864/ruby-inheritance-vs-mixins">ruby inheritance vs mixins</a> </p>
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    1. COI agree, but in his case option (b) is better. He wants to expose only a fraction of `Hash`'s methods and add new ones.
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    2. COActually, I'm interested in the general case whether or not I want to include all Hash's methods. As it happens at the moment, having them all available is fine. But, addressing Pete's solution, why add the module to an object rather than simply subclassing Hash? Would it not be more straightforward to have "class Book < Hash," adding the methods directly or via a module?
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      1. USMike Blyth
    3. COSorry for the delay, tried to expand on my answer a bit to give a little more insight into "why" I choose the option that I do in this situation. Hope it helps!
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