ruby-on-rails - Rails/Ruby 错误地显示变量未定义

Question

在调试控制台中，当应用程序运行时(使用 binding.pry 中断它)，我可以看到我的变量 Rails.configuration.hardcoded_current_user_key 已设置:

pry(#<TasksController>)> Rails.configuration.hardcoded_current_user_key
=> "dev"

但它似乎没有被定义:

pry(#<TasksController>)> defined?(Rails.configuration.hardcoded_current_user_key)
=> nil

然而它可以很好地存储和测试它的值:

pry(#<TasksController>)> tempVar = Rails.configuration.hardcoded_current_user_key
=> "dev"
pry(#<TasksController>)> defined?(tempVar)
=> "local-variable"

这是怎么回事？

Answer 1

这是因为 Rails 配置 implements respond_to? 但不是 respond_to_missing? 和 defined? 只有 recognizes respond_to_missing?:

class X
  def respond_to?(name, include_all = false)
    name == :another_secret || super
  end

  private

  def method_missing(name, *args, &block)
    case name
    when :super_secret
      'Bingo!'
    when :another_secret
      'Nope.'
    else
      super
    end
  end

  def respond_to_missing?(name, include_all = false)
    name == :super_secret || super
  end
end

x = X.new
puts x.super_secret          # => Bingo!
p defined?(x.super_secret)   # => "method"
puts x.another_secret        # => Nope.
p defined?(x.another_secret) # => nil

是recommended实现 respond_to_missing? 和 method_missing，我也想知道为什么 Rails 会那样做。