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copied!<p>So you need to learn the rules of ruby scoping.</p> <p>Ruby variables have different scope, depending on their prefix:</p> <ul> <li><code>$global_variables</code> start with a <code>$</code>, and are available to everyone.</li> <li><code>@instance_variables</code> start with a single <code>@</code>, and are stored with the current value of <code>self</code>. If two scopes share the same value of <code>self</code> (they're both instance methods, for example), then both share the same instance variables</li> <li><code>@@class_variable</code> start with <code>@@</code>, and are stored with the class. They're shared between all instances of a class - and all instances of subclasses of that class.</li> <li><code>Constants</code> start with a capital letter, and may be all caps. Like class variables, they're stored with the current <code>self.class</code>, but they also trickle up the hierarchy - so if you have a class defined in a module, the instances of the class can access the module's constants as well. Constants defined outside of a class have global scope. Note that a constant variable means that which object is bound to the constant won't change, not that the object itself won't change internal state.</li> <li><code>local_variables</code> start with a lowercase letter</li> </ul> <p>You can read more about scope <a href="http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html#UP" rel="nofollow noreferrer">here</a>.</p> <p>Local variables scoping rules are mainly standard - they're available in all subscopes of the one in which they are defined <code>except</code> when we move into a module, class, or method definition. So if we look at your code from your answer</p> <pre><code>class TestDevice attr_accessor :loghash def initialize @loghash = { } end end device = TestDevice.new class Somethingelse def self.something device.loghash='something here' # doesn't work end end </code></pre> <p>The scope of the <code>device</code> local variable defined at the toplevel does not include the <code>Somethingelse.something</code> method definition. So the <code>device</code> local variable used in the <code>Somethingelse.something</code> method definition is a different (empty) variable. If you want the scoping to work that way, you should use a constant or a global variable.</p> <pre><code>class TestDevice attr_accessor :loghash def initialize @loghash = { } end end DEVICE = TestDevice.new $has_logged = false class Somethingelse def self.something DEVICE.loghash='something here' $has_logged = true end end p DEVICE.loghash # prints `{}` p $has_logged # prints `false` Somethingelse.something p DEVICE.loghash # prints `"something here"` p $has_logged # prints `true` </code></pre>

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