Hidden features of Ruby

Continuing the "Hidden features of ..." meme, let's share the lesser-known but useful features of Ruby programming language.

Try to limit this discussion with core Ruby, without any Ruby on Rails stuff.

See also:

Hidden features of C#

Hidden features of Java

Hidden features of JavaScript

Hidden features of Ruby on Rails

Hidden features of Python

(Please, just one hidden feature per answer.)

Thank you

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从Ruby 1.9 Proc＃===是Proc＃调用的别名，这意味着Proc对象可以在case语句中使用，如下所示：

def multiple_of(factor)
  Proc.new{|product| product.modulo(factor).zero?}
end

case number
  when multiple_of(3)
    puts "Multiple of 3"
  when multiple_of(7)
    puts "Multiple of 7"
end

---

Peter Cooper has a good list of Ruby tricks. Perhaps my favorite of his is allowing both single items and collections to be enumerated. (That is, treat a non-collection object as a collection containing just that object.) It looks like this:

[*items].each do |item|
  # ...
end

---

不知道这是如何隐藏的，但是我发现它需要在一维数组中生成一个Hash：

fruit = ["apple","red","banana","yellow"]
=> ["apple", "red", "banana", "yellow"]

Hash[*fruit]    
=> {"apple"=>"red", "banana"=>"yellow"}

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