如何在 ruby​​ 中从外部访问类变量？

我正在尝试从类外部的方法访问类变量。

这是我的课：

class Book

  @@bookCount = 0
  @@allBooks = []

  def self.allBooks
    @@allBooks
  end

  def self.bookCount
    @@bookCount
  end

  attr_accessor :name,:author,:date,:genre,:rating

  def initialize(name, author, date, genre, rating)
      @name = name
      @author = author
      @date = date
      @genre = genre
      @rating = rating
      @@bookCount += 1
      @@allBooks << self
  end

end

这是尝试访问类变量@@bookCount的方法

def seeBookShelf
  if @@bookCount == 0
    puts "Your bookshelf is empty."
  else
    puts "You have " + @bookCount + " books in your bookshelf:"
    puts allBooks
  end
end

当我尝试执行该方法时，我得到以下信息：

undefined local variable or method `bookCount' for main:Object (NameError)

如何从外部访问 bookCount？

Use class_variable_get访问类外部的类变量：

class Foo
  @@a = 1
end

Foo.class_variable_get(:@@a)
=> 1