Ruby中的字符串与符号
初学Ruby的时候，往往对字符串（String类）与符号（Symbol）这两种变量类型分不清楚，其实，我们大可不必纠缠这两种变量类型的内部实现，只需记住它们的特点和区别就可以了：
1. 字符串和符号，都是Ruby中表示文本的方式
不管字符串变量也好，符号变量也好，都是用来表示文本的，它们之间，也可以互相转换（通过to_sym和to_s）：
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>> "book".to_sym
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=> :book
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>> :track.to_s
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=> "track"
2. 相同的符号是一个对象，相同的字符并不一定是一个对象
这就是符号和字符串最大的差别，符号是不可变的，不能对一个符号进行修改。所以说，两个看起来相同的符号一定是一个对象，但是说两个看起来一样的字符串是一个对象，就不对了。
这里，我们用 equal? 方法检验这一点，当两个对象相同时，equal? 返回true，反之是false：
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>> :book.equal?(:book)
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=> true
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>> "book".equal?("book")
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=> false
3. 处理符号相比字符串，占用更少的资源
这也就是为什么有些时候我们要使用符号的原因，由于字符串变量必须具有各种修改其内容的功能，所以字符串的维护和处理的开销就很大，但是有些时候，我们并不需要修改和处理创建的文本信息，这个时候用符号再好不过了。
比较典型的用法，就是在Rails中，用符号来指代散列中的参数名称：
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<% for article in @articles -%>
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<%= link_to article.title,
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:controller => "article",
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:action => "show",
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:id => article.id %>
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<% end -%>
反之，如果我们把 :controller 写成"controller"，把 :action 写成"action"，吧 :id 写成"id"，每一个循环都要创建3个新的字符对象，但是我们又不需要对这些字符串进行修改操作，白白添加了很多处理器开销，而且写成符号的形式更加简练，可以更容易分别出参数和值，何乐而不为呢。
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