ActiveSupport::Deprecation::DeprecatedConstantAccessor

DeprecatedConstantAccessor transforms a constant into a deprecated one by hooking const_missing.

It takes the names of an old (deprecated) constant and of a new constant (both in string form) and a deprecator.

The deprecated constant now returns the same object as the new one rather than a proxy object, so it can be used transparently in rescue blocks etc.

PLANETS = %w(mercury venus earth mars jupiter saturn uranus neptune pluto)

# (In a later update, the original implementation of `PLANETS` has been removed.)

PLANETS_POST_2006 = %w(mercury venus earth mars jupiter saturn uranus neptune)
include ActiveSupport::Deprecation::DeprecatedConstantAccessor
deprecate_constant 'PLANETS', 'PLANETS_POST_2006', deprecator: ActiveSupport::Deprecation.new

PLANETS.map { |planet| planet.capitalize }
# => DEPRECATION WARNING: PLANETS is deprecated! Use PLANETS_POST_2006 instead.
     (Backtrace information…)
     ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]

Class Public methods

included(base)

📝 Source code

# File activesupport/lib/active_support/deprecation/constant_accessor.rb, line 28
      def self.included(base)
        require "active_support/inflector/methods"

        extension = Module.new do
          def const_missing(missing_const_name)
            if class_variable_defined?(:@@_deprecated_constants)
              if (replacement = class_variable_get(:@@_deprecated_constants)[missing_const_name.to_s])
                replacement[:deprecator].warn(replacement[:message] || "#{name}::#{missing_const_name} is deprecated! Use #{replacement[:new]} instead.", caller_locations)
                return ActiveSupport::Inflector.constantize(replacement[:new].to_s)
              end
            end
            super
          end

          def deprecate_constant(const_name, new_constant, deprecator:, message: nil)
            class_variable_set(:@@_deprecated_constants, {}) unless class_variable_defined?(:@@_deprecated_constants)
            class_variable_get(:@@_deprecated_constants)[const_name.to_s] = { new: new_constant, message: message, deprecator: deprecator }
          end
        end
        base.singleton_class.prepend extension
      end

🔎 See on GitHub

Instance Public methods

const_missing(missing_const_name)

📝 Source code

# File activesupport/lib/active_support/deprecation/constant_accessor.rb, line 32
          def const_missing(missing_const_name)
            if class_variable_defined?(:@@_deprecated_constants)
              if (replacement = class_variable_get(:@@_deprecated_constants)[missing_const_name.to_s])
                replacement[:deprecator].warn(replacement[:message] || "#{name}::#{missing_const_name} is deprecated! Use #{replacement[:new]} instead.", caller_locations)
                return ActiveSupport::Inflector.constantize(replacement[:new].to_s)
              end
            end
            super
          end

🔎 See on GitHub

deprecate_constant(const_name, new_constant, deprecator:, message: nil)

📝 Source code

# File activesupport/lib/active_support/deprecation/constant_accessor.rb, line 42
          def deprecate_constant(const_name, new_constant, deprecator:, message: nil)
            class_variable_set(:@@_deprecated_constants, {}) unless class_variable_defined?(:@@_deprecated_constants)
            class_variable_get(:@@_deprecated_constants)[const_name.to_s] = { new: new_constant, message: message, deprecator: deprecator }
          end

🔎 See on GitHub