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PORuby: setting a new hash with an array of keys/values
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  1. PORuby: setting a new hash with an array of keys/values
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    copied!<p>I'm learning Ruby via RubyMonk. In the solution to the <a href="http://rubymonk.com/learning/books/4-ruby-primer-ascent/chapters/33-advanced-arrays/lessons/97-array-alternative-uses#solution4269" rel="nofollow">waiter robot problem</a>, there's a line of code that creates a new hash using an array:</p> <pre><code>o = Hash[*order] </code></pre> <p>given</p> <pre><code>order = [:table, 1, :sandwich, "denver", :drink, "mango shake"] </code></pre> <p>I understand what's being done here and how the splat operator works. However, I'm confused about the syntax for creating this hash. <a href="http://ruby-doc.org/core-2.0/Hash.html#method-c-5B-5D" rel="nofollow">RubyDoc</a> says that <code>::[]</code> is really the method being called, so I was able to determine that <code>o = Hash::[](*order)</code> is the same thing. But why can this be shortened to just <code>Hash[*order]</code>? Is this a special construct that gets interpreted by the parser, or is there another reason? Along the same lines, why don't any of the following work?</p> <pre><code>o = Hash.new o.[](*order) </code></pre> <p>or</p> <pre><code>o = Hash.new o[*order] </code></pre> <p>or even something like <code>o = {}[*order]</code></p> <p>I know these <em>shouldn't</em> work; I'm just not sure why. I think I'm confused by the usage of <code>Hash[*order]</code> without first instantiating a hash with <code>Hash.new</code>. Is this an example of the difference between class methods and instance methods?</p> <p>(As a side note, it seems to me that <code>o = {*order}</code> should work, but it doesn't.)</p> <p>Can someone explain what's going on here, and if there are alternate ways to add values from an array into a hash?</p>
 

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