1 files changed, 19 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/type/hash_lookup_type_map.rb b/activerecord/lib/active_record/type/hash_lookup_type_map.rb
new file mode 100644
index 0000000000..bf92680268
--- /dev/null
+++ b/activerecord/lib/active_record/type/hash_lookup_type_map.rb
@@ -0,0 +1,19 @@
+module ActiveRecord
+  module Type
+    class HashLookupTypeMap < TypeMap # :nodoc:
+      delegate :key?, to: :@mapping
+
+      def lookup(type, *args)
+        @mapping.fetch(type, proc { default_value }).call(type, *args)
+      end
+
+      def fetch(type, *args, &block)
+        @mapping.fetch(type, block).call(type, *args)
+      end
+
+      def alias_type(type, alias_type)
+        register_type(type) { |_, *args| lookup(alias_type, *args) }
+      end
+    end
+  end
+end