ActiveModel type for flags

lib/literal/flags.rb

@@ -9,7 +9,6 @@ def initialize(value = 0, **new_flags)
 		end
 
 		@value = value
-
 		freeze
 	end
 
@@ -138,6 +137,15 @@ def pack
 		[@value].pack(self.class::PACKER)
 	end
 
+	def with(**attributes)
+		new_val = attributes.reduce(value) do |value, (k, v)|
+			v ? value |= bitmap(k) : value &= ~(bitmap(k))
+			value
+		end
+
+		self.class.allocate.__initialize_from_value__(new_val)
+	end
+
 	# () -> String
 	def inspect
 		to_h.inspect
@@ -156,7 +164,7 @@ def each
 
 	# (Symbol) -> Boolean
 	def [](key)
-		@value & (2 ** self.class::FLAGS.fetch(key)) > 0
+		@value & (bitmap(key)) > 0
 	end
 
 	def |(other)
@@ -197,14 +205,19 @@ def to_a
 
 	def deconstruct_keys(keys = nil)
 		if keys
-			flags = self.class::FLAGS
 			keys.to_h do |key|
-				[key, @value & (2 ** flags.fetch(key)) > 0]
+				[key, @value & (bitmap(key)) > 0]
 			end
 		else
 			to_h
 		end
 	end
+
+	private
+
+	def bitmap(key)
+		2 ** self.class::FLAGS.fetch(key)
+	end
 end
 
 class Literal::Flags8 < Literal::Flags

lib/literal/rails.rb

@@ -5,5 +5,6 @@
 
 module Literal::Rails
 	autoload :EnumType, "literal/rails/enum_type"
+	autoload :FlagsType, "literal/rails/flags_type"
 	autoload :EnumSerializer, "literal/rails/enum_serializer"
 end

lib/literal/rails/flags_type.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+class Literal::Rails::FlagsType < ActiveModel::Type::Value
+	def initialize(flags_class)
+		@flags_class = flags_class
+		super()
+	end
+
+	def cast(value)
+		case value
+		when @flags_class
+			value
+		else
+			deserialize(value)
+		end
+	end
+
+	def serialize(value)
+		case value
+		when nil
+			nil
+		when @flags_class
+			value.to_bit_string
+		else
+			raise Literal::ArgumentError.new(
+				"Invalid value: #{value.inspect}. Expected an #{@flags_class.inspect}.",
+			)
+		end
+	end
+
+	def deserialize(value)
+		case value
+		when nil
+			nil
+		else
+			@flags_class.from_bit_string(value) || raise(
+				ArgumentError.new("Invalid value: #{value.inspect} for #{@flags_class}"),
+			)
+		end
+	end
+end

lib/literal/railtie.rb

@@ -6,8 +6,16 @@ class Literal::Railtie < Rails::Railtie
 			Literal::Rails::EnumType.new(type)
 		end
 
+		ActiveRecord::Type.register(:literal_flags) do |name, type:|
+			Literal::Rails::FlagsType.new(type)
+		end
+
 		ActiveModel::Type.register(:literal_enum) do |name, type:|
 			Literal::Rails::EnumType.new(type)
 		end
+
+		ActiveModel::Type.register(:literal_flags) do |name, type:|
+			Literal::Rails::FlagsType.new(type)
+		end
 	end
 end

test/flags.test.rb

@@ -8,6 +8,19 @@ class Example < Literal::Flags8
 	)
 end
 
+test "with" do
+	a = Example.new(italic: true, underlined: true)
+	b = a.with(bold: true, underlined: false)
+
+	refute a.bold?
+	assert a.italic?
+	assert a.underlined?
+
+	assert b.bold?
+	assert b.italic?
+	refute b.underlined?
+end
+
 test "from_array" do
 	flags = Example.from_array([false, false, false, false, false, false, false, true])