类中的成员变量可以这样声明， 但访问不能用@

大家先看下面代码：

class Person < Struct.new(:age)
	def say_age
		puts "say age: #{age}" if age != nil
	end
	
	def hello_age
		puts "hello age: #{age}" if age!=nil
	end
end

p = Person.new(30)

p.say_age
p.hello_age

p.age = 20
p.say_age
p.hello_age

输出是：
say age: 30
hello age: 30
say age: 20
hello age: 20

如果使用:

	def say_age
		puts "say age: #{@age}" if @age != nil
	end
	
	def hello_age
		puts "hello age: #{@age}" if @age!=nil
	end

那么什么都不输出，应为@age 为nil

如果使用:

	def say_age
		puts "say age: #{:age}" if :age != nil
	end
	
	def hello_age
		puts "hello age: #{:age}" if :age!=nil
	end

那么输出是：
say age: age
hello age: age
say age: age
hello age: age

:age 符号而已

ActiveRecord的低层有使用这种方式申明class

class ColumnDefinition < Struct.new(:base, :name, :type, :limit, :precision, :scale, :default, :null) #:nodoc:
..
..
..
end

文件：schema_definitions.rb
路径:%RUBY_HOME%\\lib\ruby\gems\1.8\gems\activerecord-2.0.1\lib\active_record\connection_adapters\abstract

哎哦哦。。。查了文档才知道自己自作多情了。晕

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

The Struct class is a generator of specific classes, each one of which is defined to hold a set of variables and their accessors. In these examples, we‘ll call the generated class ``CustomerClass,’’ and we‘ll show an example instance of that class as ``CustomerInst.’‘

In the descriptions that follow, the parameter symbol refers to a symbol, which is either a quoted string or a Symbol (such as :name).

例子：

   # Create a structure with a name in Struct
   Struct.new("Customer", :name, :address)    #=> Struct::Customer
   Struct::Customer.new("Dave", "123 Main")   #=> #<Struct::Customer name="Dave", address="123 Main">

   # Create a structure named by its constant
   Customer = Struct.new(:name, :address)     #=> Customer
   Customer.new("Dave", "123 Main")           #=> #<Customer name="Dave", address="123 Main">

感觉就是最纯洁的 Java Bean了。 哈哈。。。。。Ruby Stone