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POIf || has higher precedence than =, then why does `a || a = b` work?
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  1. POIf || has higher precedence than =, then why does `a || a = b` work?
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    copied!<p>I understand the difference between <code>||</code> and <code>or</code>, or <code>&amp;&amp;</code> and <code>and</code>, but what I don't understand is this:</p> <p>Consider a method that returns the value of <code>@var</code>, or initializes it if <code>@var</code> is nil for false.</p> <p>As I came from JavaScript background, I would write it like this, since <code>||</code> has higher precedence than <code>=</code>:</p> <pre><code>def some_method @var || (@var = MyClass.new) end </code></pre> <p>or use <code>or</code>, since <code>or</code> has lower precedence:</p> <pre><code>def some_method @var or @var = MyClass.new end </code></pre> <p>or more concisely:</p> <pre><code>def some_method @var ||= MyClass.new end </code></pre> <p>But it so happened that this version <strong>also works</strong>:</p> <pre><code>def some_method @var || @var = MyClass.new end </code></pre> <p>I search the web but didn't find useful results.</p> <p>Most of them just tell the difference between <code>||</code> and <code>or</code>.</p> <p>The operator precedence table clearly says that <code>||</code> has higher precedence than <code>=</code>.</p> <p>I can even do <code>a = b || c = d</code> and Ruby sees it as <code>a = (b || (c = d))</code>.</p> <p>Is this behavior documented somewhere or is it some kind of magic in Ruby?</p> <p>P.S. CoffeeScript also has the same behavior.</p> <p><strong>Update / Clarification</strong>: This question is not about short-circuit evaluation. But about operator precedence. Please let me rephrase it again:</p> <p>If <code>||</code> has higher precedence than <code>=</code>, then why does ruby sees <code>a || a = b</code> as <code>a || (a = b)</code>, but not <code>(a || a) = b</code> and raise a syntax error?</p>
 

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