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    <p>There's more to yield and blocks than mere looping. </p> <p>The series <a href="http://www.globalnerdy.com/tag/enumerating-enumerable/" rel="noreferrer">Enumerating enumerable</a> has a series of things you can do with enumerations, such as asking if a statement is true for any member of a group, or if it's true for all the members, or searching for any or all members meeting a certain condition.</p> <p>Blocks are also useful for variable scope. Rather than merely being convenient, it can help with good design. For example, the code</p> <pre><code>File.open("filename", "w") do |f| f.puts "text" end </code></pre> <p>ensures that the file stream is closed when you're finished with it, even if an exception occurs, and that the variable is out of scope once you're finished with it.</p> <p>A casual google didn't come up with a good blog post about blocks and yields in ruby. I don't know why.</p> <p><strong>Response to comment</strong>:</p> <p>I suspect it gets closed because of the block ending, not because the variable goes out of scope.</p> <p>My understanding is that nothing special happens when the last variable pointing to an object goes out of scope, apart from that object being eligible for garbage collection. I don't know how to confirm this, though.</p> <p>I can show that the file object gets closed before it gets garbage collected, which usually doesn't happen immediately. In the following example, you can see that a file object is closed in the second <code>puts</code> statement, but it hasn't been garbage collected.</p> <pre><code>g = nil File.open("/dev/null") do |f| puts f.inspect # #&lt;File:/dev/null&gt; puts f.object_id # Some number like 70233884832420 g = f end puts g.inspect # #&lt;File:/dev/null (closed)&gt; puts g.object_id # The exact same number as the one printed out above, # indicating that g points to the exact same object that f pointed to </code></pre>
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    1. PORuby's yield feature in relation to computer science
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    1. USAndrew Grimm
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    1. COHow does this ensure the file is closed when you're finished it? Ruby automatically closes it when the block ends and `f` falls out of scope?
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    2. CO@aidan The `File#open` method, when called with a block, will close the created file handle once the block has finished.
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    3. COThanks for the clarification!
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