use formatter cache for TypelessObjectResolver

Author: neuecc

src/MessagePack.UnityClient/Assets/Scripts/MessagePack/Resolvers/TypelessObjectResolver.cs

@@ -35,27 +35,35 @@ private TypelessObjectResolver()
         /// <inheritdoc />
         public IMessagePackFormatter<T> GetFormatter<T>()
         {
-            if (typeof(T).IsAbstract || typeof(T).IsInterface)
-            {
-                return new ForceTypelessFormatter<T>();
-            }
+            return Cache<T>.Formatter;
+        }
 
-            if (typeof(T) == typeof(object))
-            {
-                return (IMessagePackFormatter<T>)TypelessFormatter.Instance;
-            }
-            else
+        private static class Cache<T>
+        {
+            public static readonly IMessagePackFormatter<T> Formatter;
+
+            static Cache()
             {
-                foreach (IFormatterResolver item in Resolvers)
+                if (typeof(T).IsAbstract || typeof(T).IsInterface)
+                {
+                    Formatter = new ForceTypelessFormatter<T>();
+                }
+
+                if (typeof(T) == typeof(object))
                 {
-                    IMessagePackFormatter<T> f = item.GetFormatter<T>();
-                    if (f != null)
+                    Formatter = (IMessagePackFormatter<T>)TypelessFormatter.Instance;
+                }
+                else
+                {
+                    foreach (var item in Resolvers)
                     {
-                        return f;
+                        var f = item.GetFormatter<T>();
+                        if (f != null)
+                        {
+                            Formatter = f;
+                        }
                     }
                 }
-
-                return null;
             }
         }
     }

src/MessagePack.UnityClient/Assets/Scripts/Tests/ShareTests/MessagePackSerializerTypelessTests.cs

@@ -78,8 +78,6 @@ public void OmitAssemblyVersion()
     [Fact]
     public void SerializeInterface()
     {
-        var foo = MessagePackSerializer.Typeless.DefaultOptions.Resolver.GetFormatter<TypelessAbstract>();
-
         var v = new Holder() { T1 = new TypelessInterface { X = 999 }, T2 = new TypelessNonAbstract { X = 19, Y = 9999 } };
         var bin = MessagePackSerializer.Typeless.Serialize(v);
         var v2 = MessagePackSerializer.Typeless.Deserialize(bin).IsInstanceOf<Holder>();