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copied!<p>If all you need the hash for is membership, consider using a <a href="http://ruby-doc.org/stdlib/libdoc/set/rdoc/Set.html" rel="noreferrer"><code>Set</code></a>:</p> <blockquote> <h1>Set</h1> <p><a href="http://ruby-doc.org/stdlib/libdoc/set/rdoc/Set.html" rel="noreferrer">Set</a> implements a collection of unordered values with no duplicates. This is a hybrid of Array's intuitive inter-operation facilities and Hash's fast lookup.</p> <p><a href="http://ruby-doc.org/stdlib/libdoc/set/rdoc/Set.html" rel="noreferrer">Set</a> is easy to use with <a href="http://ruby-doc.org/core/Enumerable.html" rel="noreferrer">Enumerable</a> objects (implementing <code>each</code>). Most of the initializer methods and binary operators accept generic <a href="http://ruby-doc.org/core/Enumerable.html" rel="noreferrer">Enumerable</a> objects besides sets and arrays. An <a href="http://ruby-doc.org/core/Enumerable.html" rel="noreferrer">Enumerable</a> object can be converted to <a href="http://ruby-doc.org/stdlib/libdoc/set/rdoc/Set.html" rel="noreferrer">Set</a> using the <a href="http://ruby-doc.org/stdlib-2.2.1/libdoc/set/rdoc/Enumerable.html#method-i-to_set" rel="noreferrer"><code>to_set</code></a> method.</p> <p><a href="http://ruby-doc.org/stdlib/libdoc/set/rdoc/Set.html" rel="noreferrer">Set</a> uses Hash as storage, so you must note the following points:</p> <ul> <li>Equality of elements is determined according to <code>Object#eql?</code> and <code>Object#hash</code>.</li> <li>Set assumes that the identity of each element does not change while it is stored. Modifying an element of a set will render the set to an unreliable state.</li> <li>When a string is to be stored, a frozen copy of the string is stored instead unless the original string is already frozen.</li> </ul> <h2>Comparison</h2> <p>The comparison operators <code><</code>, <code>></code>, <code><=</code> and <code>>=</code> are implemented as shorthand for the {proper_,}{subset?,superset?} methods. However, the <code><=></code> operator is intentionally left out because not every pair of sets is comparable. ({x,y} vs. {x,z} for example)</p> <h2>Example</h2> <pre><code>require 'set' s1 = Set.new [1, 2] # -> #<Set: {1, 2}> s2 = [1, 2].to_set # -> #<Set: {1, 2}> s1 == s2 # -> true s1.add("foo") # -> #<Set: {1, 2, "foo"}> s1.merge([2, 6]) # -> #<Set: {1, 2, "foo", 6}> s1.subset? s2 # -> false s2.subset? s1 # -> true </code></pre> <p>[...]</p> <h2>Public Class Methods</h2> <h3>new(enum = nil)</h3> <p>Creates a new set containing the elements of the given enumerable object.</p> <p>If a block is given, the elements of enum are preprocessed by the given block.</p> </blockquote>

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