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PORuby: what is the pitfall in this simple code excerpt that tests variable existence
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  1. PORuby: what is the pitfall in this simple code excerpt that tests variable existence
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    copied!<p>I'm starting with Ruby, and while making some test samples, I've stumbled against an error in the code that I don't understand why it happens.</p> <p>The code pretends to tests if a variable finn is defined?() and if it is defined, then it increments it. If it isn't defined, then it will define it with value 0 (zero). As the code threw an error, I started to decompose it in small pieces and run it, to better trace where the error was comming from. The code was run in IRB irb 0.9.5(05/04/13), using ruby 1.9.1p378</p> <p>First I certify that the variable finn is not yet defined, and all is ok:</p> <pre><code>?&gt; finn NameError: undefined local variable or method `finn' for main:Object from (irb):134 from /home/paulo/.rvm/rubies/ruby-1.9.1-p378/bin/irb:15:in `&lt;main&gt;' &gt;&gt; </code></pre> <p>Then I certify that the following inline-condition executes as expected, and all is ok:</p> <pre><code>?&gt; ((defined?(finn)) ? (finn+1):(0)) =&gt; 0 </code></pre> <p>And now comes the code that throws the error: </p> <pre><code>?&gt; finn=((defined?(finn)) ? (finn+1):(0)) NoMethodError: undefined method `+' for nil:NilClass from (irb):143 from /home/paulo/.rvm/rubies/ruby-1.9.1-p378/bin/irb:15:in `&lt;main&gt;' </code></pre> <p>I was expecting that the code would not throw any error, and that after executing the variable finn would be defined with a first value of 0 (zero). But instead, the code thows the error, and finn get defined but with a value of nil.</p> <pre><code>&gt;&gt; finn =&gt; nil </code></pre> <p>Where might the error come from?!? Why does the inline-condition work alone, but not when used for the finn assignment?</p> <p>Any help apreciated :)</p>
 

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