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    <p><code>self</code> references the current object. This lends itself to many uses:</p> <h1>calling a method on the current object</h1> <pre><code>class A def initialize val @val = val end def method1 1 + self.method2() end def method2 @val*2 end end </code></pre> <p>Here running <code>A.new(1).method1()</code> will return <code>3</code>. The use of <code>self</code> is optional here - the following code is equivalent:</p> <pre><code>class A def initialize val @val = val end def method1 1 + method2() end def method2 @val*2 end end </code></pre> <p><code>self</code> is not redundant for this purpose though - operator overloading makes it neccessary:</p> <pre><code>class A def initialize val @val = val end def [] x @val + x end def method1 y [y] #returns an array! end def method2 y self.[y] #executes the [] method end end </code></pre> <p>This shows how self must be used if you want to call the current object's <code>[]</code> method.</p> <h1>referencing attributes</h1> <p>You can generate the methods to read and write to instance variables using <code>attr_accessor</code> and co. </p> <pre><code>class A attr_accessor :val def initialize val @val = val end def increment! self.val += 1 end end </code></pre> <p>Using self <em>is</em> redundant here because you can just reference the variable directly, eg. <code>@val</code>. Using the previous class, <code>A.new(1).increment!</code> would return 2.</p> <h1>method chaining</h1> <p>You can return self to provide a form of syntactical sugar known as chaining:</p> <pre><code>class A attr_reader :val def initialize val @val = val end def increment! @val += 1 self end end </code></pre> <p>Here, because we are returning the current object, methods can be chained:</p> <pre><code>A.new(1).increment!.increment!.increment!.val #returns 4 </code></pre> <h1>creating class methods</h1> <p>You can define class methods using self:</p> <pre><code>class A def self.double x x*2 end def self.quadruple x self.double(self.double(x)) end end </code></pre> <p>This will enable you to call <code>A.double(2) #= 4</code> and <code>A.quadruple(2) #=8</code>. Note that in a class method, <code>self</code> references that class because the class is the current object.</p> <h1>how the value of self is determined</h1> <p>The current value of self in a particular method is set to the object that that method was called upon. Normally this uses the '.' notation. When you run <code>some_object.some_method()</code>, self is bound to some_object for the duration of some_method, meaning that some_method can use self in one of the ways mentioned above.</p>
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