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copied!<p>There are about six options here: instance variable, class instance variable, class variable, class constant, global variable, global constant. Which to use depends on your needs.</p> <p><strong>Instance Variable</strong> - each MyClass instance gets its own options:</p> <pre><code>class MyClass def initialize @opts = ... end def my_method puts @opts[:thing] end end </code></pre> <p><strong>Class Instance Variable</strong> - single value across the class that can be reassigned:</p> <pre><code>class MyClass @opts = ... class << self attr_accessor :opts end def my_method puts self.class.opts[:thing] end end </code></pre> <p><strong>Class Variable</strong> - each MyClass <em>and all subclasses</em> share the same value (convenient syntax, but rarely a good idea):</p> <pre><code>class MyClass @@opts = ... def my_method puts @@opts[:thing] end end </code></pre> <p><strong>Class Constant</strong> - single object that may be mutated, but not re-assigned. Easily accessed from this class, accessible from others via <code>MyClass::OPTS</code>:</p> <pre><code>class MyClass OPTS = ... def my_method puts OPTS[:thing] end end </code></pre> <p><strong>Global Variable</strong> - you can only have one of these in your entire app; often global variables are ill-advised, but perhaps appropriate for a standalone application's options:</p> <pre><code>$opts = ... class MyClass def my_method puts $opts[:thing] end end </code></pre> <p><strong>Global Constant</strong> - accessed from many classes, can't be set to a new value, but may be mutated:</p> <pre><code>OPTS = ... class MyClass def my_method puts OPTS[:thing] end end </code></pre>

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