# File activesupport/lib/active_support/deprecation/method_wrappers.rb, line 52
def deprecate_methods(target_module, *method_names)
  options = method_names.extract_options!
  deprecator = options.delete(:deprecator) || self
  method_names += options.keys
  mod = nil

  method_names.each do |method_name|
    if target_module.method_defined?(method_name) || target_module.private_method_defined?(method_name)
      method = target_module.instance_method(method_name)
      target_module.redefine_method(method_name) do |*args, &block|
        deprecator.deprecation_warning(method_name, options[method_name])
        method.bind(self).call(*args, &block)
      end
    else
      mod ||= Module.new
      mod.define_method(method_name) do |*args, &block|
        deprecator.deprecation_warning(method_name, options[method_name])
        super(*args, &block)
      end
    end
  end

  target_module.prepend(mod) if mod
end

Declare that a method has been deprecated.

class Fred
  def aaa; end
  def bbb; end
  def ccc; end
  def ddd; end
  def eee; end
end

Using the default deprecator:

ActiveSupport::Deprecation.deprecate_methods(Fred, :aaa, bbb: :zzz, ccc: 'use Bar#ccc instead')
# => Fred

Fred.new.aaa
# DEPRECATION WARNING: aaa is deprecated and will be removed from Rails 5.1. (called from irb_binding at (irb):10)
# => nil

Fred.new.bbb
# DEPRECATION WARNING: bbb is deprecated and will be removed from Rails 5.1 (use zzz instead). (called from irb_binding at (irb):11)
# => nil

Fred.new.ccc
# DEPRECATION WARNING: ccc is deprecated and will be removed from Rails 5.1 (use Bar#ccc instead). (called from irb_binding at (irb):12)
# => nil

Passing in a custom deprecator:

custom_deprecator = ActiveSupport::Deprecation.new('next-release', 'MyGem')
ActiveSupport::Deprecation.deprecate_methods(Fred, ddd: :zzz, deprecator: custom_deprecator)
# => [:ddd]

Fred.new.ddd
DEPRECATION WARNING: ddd is deprecated and will be removed from MyGem next-release (use zzz instead). (called from irb_binding at (irb):15)
# => nil

Using a custom deprecator directly:

custom_deprecator = ActiveSupport::Deprecation.new('next-release', 'MyGem')
custom_deprecator.deprecate_methods(Fred, eee: :zzz)
# => [:eee]

Fred.new.eee
DEPRECATION WARNING: eee is deprecated and will be removed from MyGem next-release (use zzz instead). (called from irb_binding at (irb):18)
# => nil