Added ObjectOrId resolver

src/Discord.Net.Core/API/Common/Message.cs

@@ -27,7 +27,7 @@ namespace Discord.API
         [JsonProperty("mention_everyone")]
         public Optional<bool> MentionEveryone { get; set; }
         [JsonProperty("mentions")]
-        public Optional<User[]> UserMentions { get; set; }
+        public Optional<ObjectOrId<User>[]> UserMentions { get; set; }
         [JsonProperty("mention_roles")]
         public Optional<ulong[]> RoleMentions { get; set; }
         [JsonProperty("attachments")]

src/Discord.Net.Core/API/ObjectOrId.cs

@@ -0,0 +1,19 @@
+namespace Discord.API
+{
+    public struct ObjectOrId<T>
+    {
+        public ulong Id { get; }
+        public T Object { get; }
+
+        public ObjectOrId(ulong id)
+        {
+            Id = id;
+            Object = default(T);
+        }
+        public ObjectOrId(T obj)
+        {
+            Id = 0;
+            Object = obj;
+        }
+    }
+}

src/Discord.Net.Core/Net/Converters/DiscordContractResolver.cs

@@ -24,8 +24,9 @@ namespace Discord.Net.Converters
             {
                 JsonConverter converter;
                 var type = propInfo.PropertyType;
+                Type genericType = type.IsConstructedGenericType ? type.GetGenericTypeDefinition() : null;
 
-                if (type.IsConstructedGenericType && type.GetGenericTypeDefinition() == typeof(Optional<>))
+                if (genericType == typeof(Optional<>))
                 {
                     var typeInput = propInfo.DeclaringType;
                     var innerTypeOutput = type.GenericTypeArguments[0];
@@ -46,6 +47,20 @@ namespace Discord.Net.Converters
                         instanceField.SetValue(null, converter);
                     }
                 }
+                else if (genericType == typeof(ObjectOrId<>))
+                {
+                    var innerTypeOutput = type.GenericTypeArguments[0];
+
+                    var converterType = typeof(ObjectOrIdConverter<>).MakeGenericType(innerTypeOutput).GetTypeInfo();
+                    var instanceField = converterType.GetDeclaredField("Instance");
+                    converter = instanceField.GetValue(null) as JsonConverter;
+                    if (converter == null)
+                    {
+                        var innerConverter = GetConverter(propInfo, innerTypeOutput);
+                        converter = converterType.DeclaredConstructors.First().Invoke(new object[] { innerConverter }) as JsonConverter;
+                        instanceField.SetValue(null, converter);
+                    }
+                }
                 else
                     converter = GetConverter(propInfo, type);
 

src/Discord.Net.Core/Net/Converters/ObjectOrIdConverter.cs

@@ -0,0 +1,39 @@
+using Discord.API;
+using Newtonsoft.Json;
+using System;
+
+namespace Discord.Net.Converters
+{
+    public class ObjectOrIdConverter<T> : JsonConverter
+    {
+        internal static ObjectOrIdConverter<T> Instance;
+
+        private readonly JsonConverter _innerConverter;
+
+        public override bool CanConvert(Type objectType) => true;
+        public override bool CanRead => true;
+        public override bool CanWrite => false;
+
+        public ObjectOrIdConverter(JsonConverter innerConverter)
+        {
+            _innerConverter = innerConverter;
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            switch (reader.TokenType)
+            {
+                case JsonToken.String:
+                case JsonToken.Integer:
+                    return new ObjectOrId<T>(ulong.Parse(reader.ReadAsString()));
+                default:
+                    return new ObjectOrId<T>(serializer.Deserialize<T>(reader));
+            }
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            throw new InvalidOperationException();
+        }
+    }
+}

src/Discord.Net.Core/Net/Converters/OptionalConverter.cs

@@ -5,7 +5,7 @@ namespace Discord.Net.Converters
 {
     public class OptionalConverter<T> : JsonConverter
     {
-        public static OptionalConverter<T> Instance;
+        internal static OptionalConverter<T> Instance;
 
         private readonly JsonConverter _innerConverter;