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POBest way to extend Core class comparison methods
 

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    <p>I'd like my class to be <a href="http://blog.rubybestpractices.com/posts/rklemme/018-Complete_Class.html" rel="nofollow">complete</a> for several anticipated scenarios, including object comparison. My class is <code>Hash</code>-like in that it has a method <code>to_hash</code>, on which many of my class-completing methods are based. For example:</p> <pre><code>class Hashlike def == other if other.respond_to?(:to_hash) to_hash == other.to_hash end end end </code></pre> <p>It seems overkill to override <code>Hash#==</code> just to inject similarity into the message's superchain:</p> <pre><code>class Hash def == other # Flip the comparison other.is_a?(Hashlike) ? other == self : super end end </code></pre> <p>This will end up in stacktraces everywhere for entirely irrelevant issues. This feels invasive.</p> <p>Is there a preferred or less invasive way to make <code>Hash</code> aware of my <code>Hashlike</code>'s eligibility for comparison? And in general, is there a convention for extending core objects (<code>Hash</code>, <code>Array</code>) to receive core interface messages (<code>==</code>, <code>nil?</code>, <code>&lt;==&gt;</code>) and be aware of custom classes without leaving fingerprints all over their superchains?</p> <p><strong>Update:</strong></p> <p>The only optimization that occurs to me is to make the override call super <em>first</em> in the hopes of not choking a potentially heavily-used method with early conditional branching:</p> <pre><code>class Hash def == other # Lazily delay the comparison super or (other == self if other.is_a?(Hashlike)) end end </code></pre> <p>Some careful benchmarking (to the order of 1 billion comparisons) suggests that using either approach performs just as well as ruby's default of reversing the comparison if <code>to_hash</code> is defined on the received object, as mentioned in the answer below.</p>
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    1. USChris Keele
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