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    <p>The following solution refers to the superclass of the eigenclass. As a consequence, it has the <strong>side effect</strong> of allocating the eigenclass (detectable by <code>ObjectSpace.count_objects[:T_CLASS]</code> in MRI). But since <code>BasicObject#class</code> is only invoked on blank slate objects (i.e. objects that are not kind-of <code>Object</code>, i.e. that are not <code>Object</code><i>s</i>) the side effect also applies just for blank slate objects. For <code>Object</code><i>s</i>, the standard <code>Kernel#class</code> is invoked.</p> <pre><code>class BasicObject def class (class &lt;&lt; self; self end).superclass end end # tests: puts RUBY_VERSION # 1.9.2 class B &lt; BasicObject; end class X; end p BasicObject.new.class # BasicObject p B .new.class # B p X .new.class # X p 6.class # Fixnum p B.instance_method(:class).owner # BasicObject p X.instance_method(:class).owner # Kernel p 6.method(:class).owner # Kernel </code></pre> <p>Edit - Note: Indeed, there is an issue with <code>ActiveSupport::Duration</code>. This class uses interception (<code>method_missing</code>) for redirecting messages to the <code>:value</code> attribute. As a consequence, it provides false introspection for its instances. To preserve this falsity, it is necessary to use another name for the class map, e.g. the proposed <code>__realclass__</code>. Thus, the modified solution might look like this:</p> <pre><code>class BasicObject def __realclass__; (class &lt;&lt; self; self end).superclass end end class Object; alias __realclass__ class end </code></pre> <p>Another way of not invoking <code>class &lt;&lt; self</code> on <code>Object</code>s is via <code>Module#===</code>, as suggested by Kelvin on this page.</p>
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    1. POHow do I get the class of a BasicObject instance?
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    1. COThis is pure genius... It can even be defined after all libs are loaded. But you should define a different method name like `__realclass__`, otherwise `20.seconds.class` won't return Fixnum -- that can break a lot of code. If you do that, I'll accept your answer.
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    2. COBtw, I tried using `singleton_class.superclass` instead, but I got `TypeError: can't define singleton`. Guess BasicObject's are weird like that.
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    3. CO@Kelvin: `Fixnum`s (as well as other immediate values: `false`, `true`, `nil`, and `Symbol`s) are not blank slate objects so that `Kernel#class` gets invoked for them as before. Using `singleton_class` does not work because it is an instance method of `Kernel`.
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