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    <p>Class reopening is a good example of this. Here's a simple example:</p> <pre><code>class Integer def moxy if self.zero? self - 2 elsif self.nonzero? self + 2 end end end puts 10.moxy </code></pre> <p>By reopening a standard Ruby class - Integer - and defining a new method within it called 'moxy', we can perform a newly defined operation directly on a number. In this case, I've defined this made up 'moxy' method to subtract 2 from the Integer if it's zero and add two if it's nonzero. This makes the moxy method available to all objects of class Integer in Ruby. (Here we use the 'self' keyword to get the content of the integer object). </p> <p>As you can see, it's a very powerful feature of Ruby.</p> <p>EDIT: Some commenters have questioned whether this is really <a href="http://en.wikipedia.org/wiki/Reflection_(computer_science)" rel="nofollow noreferrer">reflection</a>. In the English language the word reflection refers to looking in on your own thoughts. And that's certainly an important aspect of reflection in programming also - using Ruby methods like is_a, kind_of, instance_of to perform runtime self-inspection. But reflection also refers to the the ability of a program to modify its own behavior at runtime. Reopening classes is one of the key examples of this. It's also called <a href="http://en.wikipedia.org/wiki/Monkey_patch" rel="nofollow noreferrer">monkey patching</a>. It's not without its risks but all I am doing is describing it here in the context of reflection, of which it is an example.</p>
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    1. POWhen you say Ruby is reflective, does this mainly refer to "duck typing"?
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    1. POWhen you say Ruby is reflective, does this mainly refer to "duck typing"?
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    1. CODefinitely a powerful feature, but are you sure it's an example of reflection? I don't know if working with self is, strictly speaking, "reflection." I thought reflection was more like when you interrogate classes and objects at runtime to find out what they are and what they can do.
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    2. COYeah, this is not really a feature of reflection, but still a cool feature.
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    3. COI understand the source of your confusion. I will edit my response to explain my reasoning for citing class reopening as an unambiguous example of reflection.
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