An example of how to deprecate constants in Ruby.

deprecator_mixin.rb

# based on ActiveSupport
# https://github.com/rails/rails/blob/6f0d1ad14b92b9f5906e44740fce8b4f1c7075dc/activesupport/lib/active_support/deprecation/constant_accessor.rb#L32
module MyLib
  module Deprecator
    def self.included(base)
      extension = Module.new do
        def const_missing(missing_const_name)
          puts "deprecator - const missing #{missing_const_name}"

          if class_variable_defined?(:@@_deprecated_constants)
            if (replacement = class_variable_get(:@@_deprecated_constants)[missing_const_name.to_s])
              puts "#{name}::#{missing_const_name} is deprecated! Use #{replacement[:new_constant]} instead"

              # this should work on Ruby >=2.0
              return replacement[:new_constant]
            end
          end

          super
        end

        def deprecate_generator(old_generator_name, new_generator_constant)
          class_variable_set(:@@_deprecated_constants, {}) unless class_variable_defined?(:@@_deprecated_constants)
          class_variable_get(:@@_deprecated_constants)[old_generator_name] = {new_constant: new_generator_constant}

          puts "DEPRECATION WARNING: #{old_generator_name} - #{new_generator_constant}"
        end
      end

      base.singleton_class.prepend extension
    end
  end

  module SomeModule
    # class IDNumber
    #   def self.foo
    #     puts "old foo"
    #   end
    # end

    class IdNumber
      def self.foo
        puts "new foo"
      end
    end

    # def self.const_missing(const_name)
    #   super unless const_name == :IDNumber
    #   warn "DEPRECATION WARNING: the class MyLib::SomeModule::IDNumber is deprecated. Use MyLib::SomeModule::IdNumber instead."
    #   IdNumber
    # end

    include Deprecator
    deprecate_generator("IDNumber", IdNumber)
  end
end

MyLib::SomeModule::IDNumber.foo
# MyLib::SomeModule::IdNumber.foo