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DeprecatedInstanceVariableProxy 将实例变量转换为已弃用的变量。它采用一个类的实例、该类上的一个方法、一个实例变量和一个弃用程序作为最后一个参数。

尝试使用已弃用的实例变量将导致弃用警告，指出该方法作为替代方法。

class Example
  def initialize
    @request = ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy.new(self, :request, :@request, ActiveSupport::Deprecation.new)
    @_request = :special_request
  end

  def request
    @_request
  end

  def old_request
    @request
  end
end

example = Example.new
# => #<Example:0x007fb9b31090b8 @_request=:special_request, @request=:special_request>

example.old_request.to_s
# => DEPRECATION WARNING: @request is deprecated! Call request.to_s instead of
   @request.to_s
   (Backtrace information…)
   "special_request"

example.request.to_s
# => "special_request"
方法
N

类公共方法

new(instance, method, var = "@#{method}", deprecator = nil)

来源：显示 | 在 GitHub 上 

# File activesupport/lib/active_support/deprecation/proxy_wrappers.rb, line 89
def initialize(instance, method, var = "@#{method}", deprecator = nil)
  @instance = instance
  @method = method
  @var = var
  ActiveSupport.deprecator.warn("DeprecatedInstanceVariableProxy without a deprecator is deprecated") unless deprecator
  @deprecator = deprecator || ActiveSupport::Deprecation._instance
end