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    <p>I think the key to understand that code (I haven't read the book) is that <code>@hide_edit_links</code> is not a boolean, it's just some kind of tag. If <code>@hide_edit_links</code> is not <code>nil</code> ( it doesn't matter which object type it's) then hide_edit_links?` will return true.</p> <p>I have to say that the code <strong>is not at all</strong> straight forward, it's definitely convoluted and complicated (probably without any reason)</p> <p>Example 1 (New instance, without <code>@hide_edit_links</code> set, so it shows link). </p> <ul> <li>The class is instantiated (this code is not in the original question, but I assume it's there), and since there's not reference to <code>@hide_edit_links</code>, the value of the instace variable is <code>nil</code></li> <li>When <code>hide_edit_links?</code> is invoked from the page, <code>@hide_edit_links</code> is nil, so <code>@hide_edit_links.nil?</code> returns true, and thus <code>not @hide_edit_links.nil?</code> is false. </li> <li>Since the page uses <code>unless hide_edit_links?</code>, it shows the link.</li> </ul> <p>Example 2 (New instance, with <code>@hide_edit_links</code> set with an object, so it doesn't show the link). </p> <ul> <li>The class is instantiated and <code>@hide_edit_links</code> is set to a value which is not <code>nil</code>.</li> <li>When <code>hide_edit_links?</code> is invoked from the page, <code>@hide_edit_links</code> is <strong>not</strong> nil, so <code>@hide_edit_links.nil?</code> returns false, and thus <code>not @hide_edit_links.nil?</code> is true. </li> <li>Since the page uses <code>unless hide_edit_links?</code>, it doesn't show the link.</li> </ul> <p>Sorry about the trivial examples... the 'feature' is not complicated, but the solution used by the author looks terribly complicated to my dumb brain.</p>
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    1. COthis helps a lot. thank you.
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    2. COI perused this book when it came out and have to agree. This is one example of many not-so-great practices within. Plus it's a bit out of date. You might do better picking up the new edition of "The Rails Way" or any number of more recent books.
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    3. COjust to give my two cents : another syntax of double negation you can run into is `!!@variable`. the "eloquent Ruby" book has a pretty clear explanation for this. Ruby works in a boolean context, but rarely using true booleans. This is bound to Ruby's philosophy : all is an object, and any object other than false and nil WILL be evaluated as true. So unless this @hide_edit_links is expected to explicitly become false at one point, it is nearly pointless to churn out such a convoluted code. I really recommend reading this book, it helped me a lot in understanding parts of the ruby idiom.
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