# File lib/hashie/extensions/coercion.rb, line 24
      def self.included(base)
        base.send :include, InstanceMethods
        base.extend ClassMethods # NOTE: we wanna make sure we first define set_value_with_coercion before extending

        base.send :alias_method, :set_value_without_coercion, :[]= unless base.method_defined?(:set_value_without_coercion)
        base.send :alias_method, :[]=, :set_value_with_coercion
      end

      module InstanceMethods
        def set_value_with_coercion(key, value)
          into = self.class.key_coercion(key) || self.class.value_coercion(value)

          unless value.nil? || into.nil?
            begin
              value = self.class.fetch_coercion(into).call(value)
            rescue NoMethodError, TypeError => e
              raise CoercionError, "Cannot coerce property #{key.inspect} from #{value.class} to #{into}: #{e.message}"
            end
          end

          set_value_without_coercion(key, value)
        end

        def custom_writer(key, value, _convert = true)
          self[key] = value
        end

        def replace(other_hash)
          (keys - other_hash.keys).each { |key| delete(key) }
          other_hash.each { |key, value| self[key] = value }
          self
        end
      end

      module ClassMethods
        attr_writer :key_coercions
        protected :key_coercions=

        # Set up a coercion rule such that any time the specified
        # key is set it will be coerced into the specified class.
        # Coercion will occur by first attempting to call Class.coerce
        # and then by calling Class.new with the value as an argument
        # in either case.
        #
        # @param [Object] key the key or array of keys you would like to be coerced.
        # @param [Class] into the class into which you want the key(s) coerced.
        #
        # @example Coerce a "user" subhash into a User object
        #   class Tweet < Hash
        #     include Hashie::Extensions::Coercion
        #     coerce_key :user, User
        #   end
        def coerce_key(*attrs)
          into = attrs.pop
          attrs.each { |key| key_coercions[key] = into }
        end

        alias coerce_keys coerce_key

        # Returns a hash of any existing key coercions.
        def key_coercions
          @key_coercions ||= {}
        end

        # Returns the specific key coercion for the specified key,
        # if one exists.
        def key_coercion(key)
          key_coercions[key.to_sym]
        end

        # Set up a coercion rule such that any time a value of the
        # specified type is set it will be coerced into the specified
        # class.
        #
        # @param [Class] from the type you would like coerced.
        # @param [Class] into the class into which you would like the value coerced.
        # @option options [Boolean] :strict (true) whether use exact source class only or include ancestors
        #
        # @example Coerce all hashes into this special type of hash
        #   class SpecialHash < Hash
        #     include Hashie::Extensions::Coercion
        #     coerce_value Hash, SpecialHash
        #
        #     def initialize(hash = {})
        #       super
        #       hash.each_pair do |k,v|
        #         self[k] = v
        #       end
        #     end
        #   end
        def coerce_value(from, into, options = {})
          options = { strict: true }.merge(options)

          if ABSTRACT_CORE_TYPES.key? from
            ABSTRACT_CORE_TYPES[from].each do |type|
              coerce_value type, into, options
            end
          end

          if options[:strict]
            strict_value_coercions[from] = into
          else
            while from.superclass && from.superclass != Object
              lenient_value_coercions[from] = into
              from = from.superclass
            end
          end
        end

        # Return all value coercions that have the :strict rule as true.
        def strict_value_coercions
          @strict_value_coercions ||= {}
        end

        # Return all value coercions that have the :strict rule as false.
        def lenient_value_coercions
          @lenient_value_coercions ||= {}
        end

        # Fetch the value coercion, if any, for the specified object.
        def value_coercion(value)
          from = value.class
          strict_value_coercions[from] || lenient_value_coercions[from]
        end

        def fetch_coercion(type)
          return type if type.is_a? Proc
          coercion_cache[type]
        end

        def coercion_cache
          @coercion_cache ||= ::Hash.new do |hash, type|
            hash[type] = build_coercion(type)
          end
        end

        def build_coercion(type)
          if type.is_a? Enumerable
            if type.class <= ::Hash
              type, key_type, value_type = type.class, *type.first
              build_hash_coercion(type, key_type, value_type)
            else # Enumerable but not Hash: Array, Set
              value_type = type.first
              type = type.class
              build_container_coercion(type, value_type)
            end
          elsif CORE_TYPES.key? type
            build_core_type_coercion(type)
          elsif type.respond_to? :coerce
            lambda do |value|
              return value if value.is_a? type
              type.coerce(value)
            end
          elsif type.respond_to? :new
            lambda do |value|
              return value if value.is_a? type
              type.new(value)
            end
          else
            raise TypeError, "#{type} is not a coercable type"
          end
        end

        def build_hash_coercion(type, key_type, value_type)
          key_coerce = fetch_coercion(key_type)
          value_coerce = fetch_coercion(value_type)
          lambda do |value|
            type[value.map { |k, v| [key_coerce.call(k), value_coerce.call(v)] }]
          end
        end

        def build_container_coercion(type, value_type)
          value_coerce = fetch_coercion(value_type)
          lambda do |value|
            type.new(value.map { |v| value_coerce.call(v) })
          end
        end

        def build_core_type_coercion(type)
          name = CORE_TYPES[type]
          lambda do |value|
            return value if value.is_a? type
            return value.send(name)
          end
        end

        def inherited(klass)
          super

          klass.key_coercions = key_coercions.dup
        end
      end
    end