Make Language objects comparable (only) depending on their 639-3 code

lib/languages/language.rb

@@ -3,6 +3,8 @@
 module Languages
   # Language defined in ISO 639-3
   class Language
+    include Comparable
+
     attr_reader :iso639_1, :iso639_2b, :iso639_2t, :iso639_3, :scope, :type, :name # , :comment
 
     def initialize(csv_attributes) # rubocop:disable Metrics/AbcSize
@@ -43,6 +45,16 @@ def to_s
       end
     end
 
+    def ==(other)
+      other.class == self.class && other.iso639_3 == iso639_3
+    end
+
+    alias eql? ==
+
+    def hash
+      iso639_3.hash
+    end
+
     def <=>(other)
       other.iso639_3 <=> iso639_3
     end

sig/languages.rbs

@@ -55,6 +55,9 @@ module Languages
     def living?: () -> bool
     def special?: () -> bool
 
+    def ==: (untyped) -> bool
+    alias eql? ==
+    def hash: () -> Integer
     def <=>: (Language) -> Integer
   end
 end

test/test_language.rb

@@ -19,6 +19,12 @@ def test_that_it_has_a_name
     assert_instance_of String, @language.name
   end
 
+  def test_equality_depends_on_iso639_3
+    other_language = ::Languages::Language.new(id: 'tlh', part2b: nil, part2t: nil, part1: nil, scope: nil,
+                                               language_type: nil, ref_name: nil)
+    assert @language == other_language
+  end
+
   ::Languages::TYPES.each do |type|
     define_method "test_that_respond_to_#{type}?" do
       assert_respond_to @language, "#{type}?"