>> s="foobar"
>> s.class
=> String
>> s=String.new("foobar")
>> s=="foobar"
=> true
>> a=Array.new([1,2,3])
=> [1,2,3]
>> h=Hash.new
=> {}
>> h[:foo]
=> nil
>> h=Hash.new(0) #默认值为0
=> {}
>> h[:foo]
=> 0

>> s.class.superclass
=> Object
>> s.class.superclass.superclass
=> BasicObject
>> s.class.superclass.superclass.superclass
=> nil

class User
    attr_accessor :anme, :email
    
    def initialize(attributes={})
        @name=attributes[:name]
        @email=attributes[:email]
    end
   
    def formatted_email
        "#{@name} <#{@email}"
    end
end