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

Namespace
Methods
N
Included Modules
Constants
DEFAULT_BEHAVIORS = { :stderr => Proc.new { |message, callstack| $stderr.puts(message) $stderr.puts callstack.join("\n ") if debug }, :log => Proc.new { |message, callstack| logger = if defined?(Rails) && Rails.logger Rails.logger else require 'active_support/logger' ActiveSupport::Logger.new($stderr) end logger.warn message logger.debug callstack.join("\n ") if debug }, :notify => Proc.new { |message, callstack| ActiveSupport::Notifications.instrument("deprecation.rails", :message => message, :callstack => callstack) }, :silence => Proc.new { |message, callstack| } }
 

Default warning behaviors per Rails.env.
Attributes
[RW] deprecation_horizon

The version the deprecated behavior will be removed, by default.
Class Public methods
new(deprecation_horizon = '4.1', gem_name = 'Rails')

It accepts two parameters on initialization. The first is an version of library and the second is an library name

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

Source: show | on GitHub 

# File activesupport/lib/active_support/deprecation.rb, line 35
def initialize(deprecation_horizon = '4.1', 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