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PORuby and duck typing: design by contract impossible?
 

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    <p>Method signature in Java:</p> <pre><code>public List&lt;String&gt; getFilesIn(List&lt;File&gt; directories) </code></pre> <p>similar one in ruby</p> <pre><code>def get_files_in(directories) </code></pre> <p>In the case of Java, the type system gives me information about what the method expects and delivers. In Ruby's case, I have <strong>no</strong> clue what I'm supposed to pass in, or what I'll expect to receive.</p> <p>In Java, the object must formally implement the interface. In Ruby, the object being passed in must respond to whatever methods are called in the method defined here. </p> <p>This seems highly problematic:</p> <ol> <li>Even with 100% accurate, up-to-date documentation, the Ruby code has to essentially expose its implementation, breaking encapsulation. "OO purity" aside, this would seem to be a maintenance nightmare.</li> <li>The Ruby code gives me <strong>no</strong> clue what's being returned; I would have to essentially experiment, or read the code to find out what methods the returned object would respond to.</li> </ol> <p>Not looking to debate static typing vs duck typing, but looking to understand how you maintain a production system where you have almost no ability to design by contract.</p> <h3>Update</h3> <p>No one has really addressed the exposure of a method's internal implementation via documentation that this approach requires. Since there are no interfaces, if I'm not expecting a particular type, don't I have to itemize every method I might call so that the caller knows what can be passed in? Or is this just an edge case that doesn't really come up?</p>
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