Not displaying it's corresponding values with it's key for Hash

Question

Ok i am not here to ask for an answer. But to be honest i am not really good in class variable. So i would appreciate you can guide me along with this piece of code.

I have read on class variable at those docs. I some what kind of understand it. But it comes to applying it for my own use. I would get confused.

class Square

   @@sqArray = {}

    #attr_accessor :length

   def initialize
      if defined?(@@length)
        randno = "%s" % [rand(20)]
        @@length = randno.to_i
        @@sqArray = @@length

    else 
        randno = "%s" % [rand(20)]
        @@length = randno.to_i
        @@sqArray = @@length
    end
   end

   def Area
         @@area = @@length * @@length
         return @@area
         @@sqArray[@@length.to_sym] = @@area
         puts @@sqArray
   end  
   end

        s1 = Square.new
        puts s1.Area

Let me explain this piece of code. Basically every time i create a Square object it would go to initialize method. A random number will be generated and pass it to @@length, and @@length will be assigned to hash @@sqArray as it's key. But now the problem is when i create a new object s1. When i want to display the Area i want to test out to print the hash @@sqArray with it's length as it's key and area as it's value. But now the problem is only returning it's area only. e.g 114 only. suppose to be e.g [ 24 => 114]

Answer 1

在定义对象的属性（即它的length）时，正确的方法是使用实例变量，而不是类变量。这是因为（在您的特定示例中），length是特定square的属性，而不适用于所有正方形。您的代码应如下所示：

class Square
  def initialize(length = rand(20))
    @length = length
  end

  def area
    @length * @length
  end
end

s1 = Square.new
puts s1.area

现在，我有点不清楚你打算通过使用那个类变量@@sqArray来实现什么目的 - 但是例如，你可以使用这个商店列出所有已定义的Square：< / p>

class Square
  @@squares_list = []
  def self.all_known
    @@squares_list
  end

  def initialize(length = rand(20))
    @length = length
    @@squares_list << self
  end

  def area
    @length * @length
  end
end

这将允许您编写如下代码：

s1 = Square.new     #=> #<Square:0x0000000132dbc8 @length=9>
s2 = Square.new(20) #=> #<Square:0x000000012a1038 @length=20>
s1.area             #=> 81
s2.area             #=> 400
Square.all_known    #=> [#<Square:0x0000000132dbc8 @length=9>, #<Square:0x000000012a1038 @length=20>]

类变量有一些奇怪的行为和有限的用例;我一般建议你在开始学习Ruby时避免使用它们。请仔细阅读ruby style guide，了解有关最佳做法的一些常见惯例 - 包括变量/方法命名（使用snake_case而非camelCase或PascalCase），空格等。< / p>