blocks|key|305139|text|从Struct文档中：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|305140|305141|结构是一种方便的方法，可以使用访问器方法将许多属性捆绑在一起，而不必编写显式的类。|blockquote|305142|305143|305144|另一方面，一个Hash|305145|305146|散列是键-值对的集合。它类似于Array，不同之处在于索引是通过任何对象类型的任意键完成的，而不是整数索引。按键或值遍历散列的顺序可能看起来是任意的，通常不是插入顺序。|305147|305148|305149|主要区别在于您访问数据的方式。|305150|ruby-1.9.1-p378+>+Point+=+Struct.new(:x,+:y)
+=>+Point+
ruby-1.9.1-p378+>+p+=+Point.new(4,5)
+=>+#<struct+Point+x=4,+y=5>+
ruby-1.9.1-p378+>+p.x
+=>+4+
ruby-1.9.1-p378+>+p.y
+=>+5+
ruby-1.9.1-p378+>+p+=+{:x+=>+4,+:y+=>+5}
+=>+{:x=>4,+:y=>5}+
ruby-1.9.1-p378+>+p.x
NoMethodError:+undefined+method+`x'+for+{:x=>4,+:y=>5}:Hash
++++from+(irb):7
++++from+/Users/mr/.rvm/rubies/ruby-1.9.1-p378/bin/irb:17:in+`<main>'
ruby-1.9.1-p378+>+p[:x]
+=>+4+
ruby-1.9.1-p378+>+p[:y]
+=>+5+|code-block|syntax|javascript|305151|简而言之，当你想要一个"plain+old+data"+structure类时，你可以创建一个新的Struct+(可选的，意图是用更多的方法来扩展它)，当你根本不需要一个正式类型时，你可以使用Hash。|305152|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/core/classes/Struct.html|1|http://ruby-doc.org/core/classes/Hash.html|2|http://en.wikipedia.org/wiki/Plain_old_data_structure^0|1|6|0|0|0|0|0|0|7|4|1|0|0|0|0|0|0|0|B|Q|2|0^^$0|@$1|2|3|4|5|6|7|1B|8|@]|9|@$A|1C|B|1D|1|1E]]|C|$]]|$1|D|3|-4|5|6|7|1F|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|1G|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|1H|8|@]|9|@]|C|$]]|$1|I|3|-4|5|6|7|1I|8|@]|9|@]|C|$]]|$1|J|3|K|5|6|7|1J|8|@]|9|@$A|1K|B|1L|1|1M]]|C|$]]|$1|L|3|-4|5|6|7|1N|8|@]|9|@]|C|$]]|$1|M|3|N|5|G|7|1O|8|@]|9|@]|C|$]]|$1|O|3|-4|5|6|7|1P|8|@]|9|@]|C|$]]|$1|P|3|-4|5|6|7|1Q|8|@]|9|@]|C|$]]|$1|Q|3|R|5|6|7|1R|8|@]|9|@]|C|$]]|$1|S|3|T|5|U|7|1S|8|@]|9|@]|C|$V|W]]|$1|X|3|Y|5|6|7|1T|8|@]|9|@$A|1U|B|1V|1|1W]]|C|$]]|$1|Z|3|-4|5|6|7|1X|8|@]|9|@]|C|$]]]|10|$11|$5|12|13|14|C|$15|16]]|17|$5|12|13|14|C|$15|18]]|19|$5|12|13|14|C|$15|1A]]]]

From the <a href="http://ruby-doc.org/core/classes/Struct.html" rel="noreferrer">Struct</a> documentation:

<blockquote>
 A Struct is a convenient way to bundle a number of attributes together, using accessor methods, without having to write an explicit class. 
</blockquote>

On the other hand, a <a href="http://ruby-doc.org/core/classes/Hash.html" rel="noreferrer">Hash</a>:

<blockquote>
 A Hash is a collection of key-value pairs. It is similar to an Array, except that indexing is done via arbitrary keys of any object type, not an integer index. The order in which you traverse a hash by either key or value may seem arbitrary, and will generally not be in the insertion order. 
</blockquote>

The main difference is how you access your data.

<pre><code>ruby-1.9.1-p378 &gt; Point = Struct.new(:x, :y)
 =&gt; Point 
ruby-1.9.1-p378 &gt; p = Point.new(4,5)
 =&gt; #&lt;struct Point x=4, y=5&gt; 
ruby-1.9.1-p378 &gt; p.x
 =&gt; 4 
ruby-1.9.1-p378 &gt; p.y
 =&gt; 5 
ruby-1.9.1-p378 &gt; p = {:x =&gt; 4, :y =&gt; 5}
 =&gt; {:x=&gt;4, :y=&gt;5} 
ruby-1.9.1-p378 &gt; p.x
NoMethodError: undefined method `x' for {:x=&gt;4, :y=&gt;5}:Hash
 from (irb):7
 from /Users/mr/.rvm/rubies/ruby-1.9.1-p378/bin/irb:17:in `&lt;main&gt;'
ruby-1.9.1-p378 &gt; p[:x]
 =&gt; 4 
ruby-1.9.1-p378 &gt; p[:y]
 =&gt; 5 
</code></pre>

In short, you would make a new Struct when you want a class that's a <a href="http://en.wikipedia.org/wiki/Plain_old_data_structure" rel="noreferrer">"plain old data" structure</a> (optionally with the intent of extending it with more methods), and you would use a Hash when you don't need a formal type at all.

blocks|key|3247302|text|Structs与使用hashmaps有以下不同之处(除了代码的外观之外)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3247303|3247304|结构有一组固定的属性，而您向散列中添加了新的键。|unordered-list-item|3247305|调用在结构的实例上不存在的属性将导致NoMethodError，而从散列中获取不存在的键的值将只返回nil。|3247306|不同结构的两个实例永远不会相等，即使结构具有相同的属性并且实例具有相同的值(即Struct.new(:x).new(42)+==+Struct.new(:x).new(42)为false，而Foo+=+Struct.new(:x);+Foo.new(42)==Foo.new(42)为true)。|offset|length|style|CODE|3247307|结构的to_a方法返回一个值数组，虽然散列上的to_a会得到键值对的数组(其中“|3247308|”表示“双元素数组”)，但|3247309|如果为Foo+=+Struct.new(:x,+:y,+:z)，则可以执行Foo.new(1,2,3)来创建Foo的实例，而不必拼写属性名称。|3247310|3247311|所以回答这个问题:当你想用一组已知的属性来建模对象时，使用structs。当你想任意使用hashmap建模时(例如，计算每个单词在字符串中出现的频率或将昵称映射为全名等肯定不是结构的工作，而使用姓名、年龄和地址建模一个人将非常适合Person+=+Struct.new(name,+age,+address))。|3247312|作为附注:C结构与ruby结构几乎没有关系，所以不要让自己对此感到困惑。|3247313|entityMap^0|0|0|0|0|13|1C|2N|1A|0|3|4|N|4|0|0|3|S|11|E|1I|3|0|0|37|13|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|11|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|12|8|@]|9|@]|A|$]]|$1|F|3|G|5|E|7|13|8|@]|9|@]|A|$]]|$1|H|3|I|5|E|7|14|8|@$J|15|K|16|L|M]|$J|17|K|18|L|M]]|9|@]|A|$]]|$1|N|3|O|5|E|7|19|8|@$J|1A|K|1B|L|M]|$J|1C|K|1D|L|M]]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1E|8|@]|9|@]|A|$]]|$1|R|3|S|5|E|7|1F|8|@$J|1G|K|1H|L|M]|$J|1I|K|1J|L|M]|$J|1K|K|1L|L|M]]|9|@]|A|$]]|$1|T|3|-4|5|6|7|1M|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1N|8|@$J|1O|K|1P|L|M]]|9|@]|A|$]]|$1|W|3|X|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1R|8|@]|9|@]|A|$]]]|Z|$]]

Structs differ from using hashmaps in the following ways (in addition to how the code looks):

<ul>
<li>A struct has a fixed set of attributes, while you add new keys to a hash.</li>
<li>Calling an attribute that does not exist on an instance of a struct will cause a NoMethodError, while getting the value for a non-existing key from a hash will just return nil.</li>
<li>Two instances of different structs will never be equal even if the structs have the same attributes and the instances have the same values (i.e. <code>Struct.new(:x).new(42) == Struct.new(:x).new(42)</code> is false, whereas <code>Foo = Struct.new(:x); Foo.new(42)==Foo.new(42)</code> is true).</li>
<li>The <code>to_a</code> method for structs returns an array of values, while <code>to_a</code> on a hash gets you an array of key-value-pairs (where "pair" means "two-element array")</li>
<li>If <code>Foo = Struct.new(:x, :y, :z)</code> you can do <code>Foo.new(1,2,3)</code> to create an instance of <code>Foo</code> without having to spell out the attribute names.</li>
</ul>

So to answer the question: When you want to model objects with a known set of attributes, use structs. When you want to model arbitrary use hashmaps (e.g. counting how often each word occurs in a string or mapping nicknames to full names etc. are definitely not jobs for a struct, while modeling a person with a name, an age and an address would be a perfect fit for <code>Person = Struct.new(name, age, address)</code>).

As a sidenote: C structs have little to nothing to do with ruby structs, so don't let yourself get confused by that.

blocks|key|303128|text|我知道这个问题几乎得到了很好的回答，但令人惊讶的是，没有人谈到Struct最大的区别之一和真正的好处。我猜这就是为什么somebody+is+still+asking。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|303129|303130|我理解其中的区别，但是当Hash可以做同样的事情并且更容易处理时，使用Struct而不是Hash的真正优势是什么？似乎Struct是一种多余的东西。|blockquote|303131|303132|303133|Struct是faster。|BOLD|303134|require+'benchmark'

Benchmark.bm+10+do+%7Cbench%7C
++bench.report+"Hash:+"+do
++++50_000_000.times+do+{+name:+"John+Smith",+age:+45+}+end
++end

++bench.report+"Struct:+"+do
++++klass+=+Struct.new(:name,+:age)
++++50_000_000.times+do+klass.new("John+Smith",+45)+end
++end

end

#+ruby+2.2.2p95+(2015-04-13+revision+50295)+[x64-mingw32].
#+++++++++++++++++user+++++system++++++total++++++++real
#+Hash:+++++++22.340000+++0.016000++22.356000+(+24.260674)
#+Struct:+++++12.979000+++0.000000++12.979000+(+14.095455)

#+ruby+2.2.2p95+(2015-04-13+revision+50295)+[x86_64-darwin11.0]
#+
#++++++++++++++++++user+++++system++++++total++++++++real
#+Hash:+++++++31.980000+++0.060000++32.040000+(+32.039914)
#+Struct:+++++16.880000+++0.010000++16.890000+(+16.886061)|code-block|syntax|javascript|303135|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/3275594/when-to-use-struct-instead-of-hash-in-ruby#comment38680650_3275624^0|V|6|1N|O|0|0|0|0|0|0|0|6|7|6|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@$9|14|A|15|1|16]]|E|$]]|$1|F|3|-4|5|6|7|17|8|@]|D|@]|E|$]]|$1|G|3|H|5|I|7|18|8|@]|D|@]|E|$]]|$1|J|3|-4|5|6|7|19|8|@]|D|@]|E|$]]|$1|K|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|1B|8|@$9|1C|A|1D|B|C]|$9|1E|A|1F|B|N]]|D|@]|E|$]]|$1|O|3|P|5|Q|7|1G|8|@]|D|@]|E|$R|S]]|$1|T|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|U|$V|$5|W|X|Y|E|$Z|10]]]]

I know this question was almost well-answered, but surprisingly nobody has talked about one of the biggest differences and the real benefits of <code>Struct</code>. And I guess that's why <a href="https://stackoverflow.com/questions/3275594/when-to-use-struct-instead-of-hash-in-ruby#comment38680650_3275624">somebody is still asking</a>.

<blockquote>
 I understand the differences, but what's the real advantage to using a Struct over a Hash, when a Hash can do the same thing, and is simpler to deal with? Seems like Structs are kind of superfluous.
</blockquote>

<code>Struct</code> is faster.

<pre><code>require 'benchmark'

Benchmark.bm 10 do |bench|
 bench.report "Hash: " do
 50_000_000.times do { name: "John Smith", age: 45 } end
 end

 bench.report "Struct: " do
 klass = Struct.new(:name, :age)
 50_000_000.times do klass.new("John Smith", 45) end
 end

end

# ruby 2.2.2p95 (2015-04-13 revision 50295) [x64-mingw32].
# user system total real
# Hash: 22.340000 0.016000 22.356000 ( 24.260674)
# Struct: 12.979000 0.000000 12.979000 ( 14.095455)

# ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-darwin11.0]
# 
# user system total real
# Hash: 31.980000 0.060000 32.040000 ( 32.039914)
# Struct: 16.880000 0.010000 16.890000 ( 16.886061)
</code></pre>

blocks|key|303137|text|另一个主要区别是您可以将行为方法添加到Struct中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|303138|+Customer+=+Struct.new(:name,+:address)+do

++def+greeting;+"Hello+#{name}!"+;+end

end

Customer.new("Dave",+"123+Main").greeting++#+=>+"Hello+Dave!"|code-block|syntax|javascript|303139|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

One more main difference is you can add behavior methods to a Struct. 

<pre><code> Customer = Struct.new(:name, :address) do

 def greeting; "Hello #{name}!" ; end

end

Customer.new("Dave", "123 Main").greeting # =&gt; "Hello Dave!"
</code></pre>

blocks|key|3033301|text|如果您只是打算封装数据，那么Hash+(或数组Hash)就可以了。如果您计划让数据操作其他数据或与其他数据交互，那么Struct可以提供一些有趣的可能性：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3033302|Point+=+Struct.new(:x,+:y)
point_a+=+Point.new(0,0)
point_b+=+Point.new(2,3)

class+Point
++def+distance_to+another_point
++++Math.sqrt((self.x+-+another_point.x)**2+%2B+(self.y+-+another_point.y)**2)
++end
end

puts+point_a.distance_to+point_b|code-block|syntax|javascript|3033303|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If you're just going to encapsulate the data, then a Hash (or an Array of Hashes) are fine. If you're planning to have the data manipulate or interact with other data, then a Struct can open some interesting possibilities:

<pre><code>Point = Struct.new(:x, :y)
point_a = Point.new(0,0)
point_b = Point.new(2,3)

class Point
 def distance_to another_point
 Math.sqrt((self.x - another_point.x)**2 + (self.y - another_point.y)**2)
 end
end

puts point_a.distance_to point_b
</code></pre>

I don't have much programming experience. But, to me, Struct seems somewhat similar to Hash.

<ul>
<li>What can Struct do well?</li>
<li>Is there anything Struct can do, that Hash cannot do?</li>
</ul>

After googling, the concept of Struct is important in C, but I don't know much about C.

When to use Struct instead of Hash in Ruby?

我没有多少编程经验。但是，在我看来，Struct似乎有点类似于Hash。什么结构可以做得很好？有没有什么结构可以做，而哈希不能做？在googling上搜索后，Struct的概念在C中很重要，但我对C了解不多。

问什么时候在Ruby中使用Struct而不是Hash？
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