🔧⚡️ Store Config attr_accessors in a Struct

Config values are stored in a struct rather than ivars to simplify:
* ensuring that all config objects share a single object shape
* querying only locally configured values, e.g for inspection.

Author: nevans

lib/net/imap/config.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 # :markup: markdown
 
+require_relative "config/attr_accessors"
+
 module Net
   class IMAP
 
@@ -11,6 +13,7 @@ class IMAP
     # *NOTE:* Updates to config objects are not synchronized for thread-safety.
     #
     class Config
+      include AttrAccessors
 
       # The debug mode (boolean)
       attr_accessor :debug

lib/net/imap/config/attr_accessors.rb

@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+require "forwardable"
+
+module Net
+  class IMAP
+    class Config
+
+      # Config values are stored in a struct rather than ivars to simplify:
+      # * ensuring that all config objects share a single object shape
+      # * querying only locally configured values, e.g for inspection.
+      module AttrAccessors
+        module Macros # :nodoc: internal API
+          def attr_accessor(name) AttrAccessors.attr_accessor(name) end
+        end
+        private_constant :Macros
+
+        def self.included(mod)
+          mod.extend Macros
+        end
+        private_class_method :included
+
+        extend Forwardable
+
+        def self.attr_accessor(name) # :nodoc: internal API
+          name = name.to_sym
+          def_delegators :data, name, :"#{name}="
+        end
+
+        def self.attributes
+          instance_methods.grep(/=\z/).map { _1.to_s.delete_suffix("=").to_sym }
+        end
+        private_class_method :attributes
+
+        def self.struct # :nodoc: internal API
+          unless defined?(self::Struct)
+            const_set :Struct, Struct.new(*attributes)
+          end
+          self::Struct
+        end
+
+        def initialize # :notnew:
+          super()
+          @data = AttrAccessors.struct.new
+        end
+
+        # Freezes the internal attributes struct, in addition to +self+.
+        def freeze
+          data.freeze
+          super
+        end
+
+        protected
+
+        attr_reader :data # :nodoc: internal API
+
+        private
+
+        def initialize_dup(other)
+          super
+          @data = other.data.dup
+        end
+
+      end
+    end
+  end
+end