class ActiveSupport::Deprecation

variables, objects and constants.
Deprecation specifies the API used by Rails to deprecate methods, instance

def initialize(deprecation_horizon = '5.1', gem_name = 'Rails')

ActiveSupport::Deprecation.new('2.0', 'MyLibrary')

and the second is a library name
It accepts two parameters on initialization. The first is a version of library 
def initialize(deprecation_horizon = '5.1', gem_name = 'Rails')
  self.gem_name = gem_name
  self.deprecation_horizon = deprecation_horizon
  # By default, warnings are not silenced and debugging is off.
  self.silenced = false
  self.debug = false
end