This DeprecatedConstantProxy transforms constant to deprecated constant.
OLD_CONST = ActiveSupport::Deprecation::DeprecatedConstantProxy.new('OLD_CONST', 'NEW_CONST') OLD_CONST = ActiveSupport::Deprecation::DeprecatedConstantProxy.new('OLD_CONST', 'NEW_CONST', deprecator_instance)
When someone use old constant this will trigger warn method on deprecator_instance.
Default deprecator is ActiveSupport::Deprecation.