Ruby Metaprogramming：如何打印局部变量和在构造函数中定义的类变量答案

【问题标题】：Ruby Metaprogramming : How to print local variable by and class variable defined instide constructorRuby Metaprogramming：如何打印局部变量和在构造函数中定义的类变量
【发布时间】：2017-09-30 10:56:58
【问题描述】：

我正在学习元编程并尝试解决这里给出的难题http://ruby-metaprogramming.rubylearning.com/html/Exercise_1.html

class A
  def initialize
    @a = 11
    @@a = 22
    a = 33
  end
  @a = 1
  @@a = 2
  a = 3
end

Given the above class i have to print below ouptput

1
2
3
11
22
33

我无法打印 33 和 3 。谁能帮我打印一下？

【问题讨论】：

标签： ruby metaprogramming

【解决方案1】：

请检查此要点：https://gist.github.com/greggawatt/8994520

$results = []

$results << class A
  def initialize
    @a = 11
    @@a = 22
    a = 33
  end
  @a = 1
  @@a = 2
  a = 3
end

这里我们使用instance_variable_get返回给定实例变量的值，使用class_variable_get检索类变量的值。

$results << A.instance_variable_get(:@a)
$results << A.class_variable_get(:@@a)

puts $results.sort!

# 1
# 2
# 3

class B < A
  def initialize
    $results << super
  end
end


A.new
# define class A and get the instance variable 11 from the initialize method
$results <<  A.new.instance_variable_get(:@a)
# define class A and get the instance variable 22 from the initialize method
$results <<  A.class_variable_get(:@@a)

# here class B inherits from class A and use the `super` to call the `initialize` method of the parent class A, 
# this way you can retrieve the instance variable `a = 33` from the initialize method on Class A.
B.new

puts $results.sort!

# 1
# 2
# 3
# 11
# 22
# 33

【讨论】：