This DeprecatedObjectProxy transforms object to deprecated object.

@old_object = DeprecatedObjectProxy.new(Object.new, "Don't use this object anymore!")
@old_object = DeprecatedObjectProxy.new(Object.new, "Don't use this object anymore!", deprecator_instance)

When someone executes any method except inspect on proxy object this will trigger warn method on deprecator_instance.

Default deprecator is ActiveSupport::Deprecation

Methods
N
Class Public methods
new(object, message, deprecator = ActiveSupport::Deprecation.instance)

Source: show | on GitHub 

# File activesupport/lib/active_support/deprecation/proxy_wrappers.rb, line 38
def initialize(object, message, deprecator = ActiveSupport::Deprecation.instance)
  @object = object
  @message = message
  @deprecator = deprecator
end