Added IGuildUser.ChangeRolesAsync

src/Discord.Net.Core/Extensions/GuildUserExtensions.cs

@@ -6,14 +6,23 @@ namespace Discord
 {
     public static class GuildUserExtensions
     {
+        //TODO: Should we remove Add/Remove? Encourages race conditions.
         public static Task AddRolesAsync(this IGuildUser user, params IRole[] roles)
-            => AddRolesAsync(user, (IEnumerable<IRole>)roles);
+            => ChangeRolesAsync(user, add: roles);
         public static Task AddRolesAsync(this IGuildUser user, IEnumerable<IRole> roles)
-            => user.ModifyAsync(x => x.RoleIds = user.RoleIds.Concat(roles.Select(y => y.Id)).ToArray());
-
+            => ChangeRolesAsync(user, add: roles);
         public static Task RemoveRolesAsync(this IGuildUser user, params IRole[] roles)
-            => RemoveRolesAsync(user, (IEnumerable<IRole>)roles);
+            => ChangeRolesAsync(user, remove: roles);
         public static Task RemoveRolesAsync(this IGuildUser user, IEnumerable<IRole> roles)
-            => user.ModifyAsync(x => x.RoleIds = user.RoleIds.Except(roles.Select(y => y.Id)).ToArray());
+            => ChangeRolesAsync(user, remove: roles);
+        public static async Task ChangeRolesAsync(this IGuildUser user, IEnumerable<IRole> add = null, IEnumerable<IRole> remove = null)
+        {
+            IEnumerable<ulong> roleIds = user.RoleIds;
+            if (remove != null)
+                roleIds = roleIds.Except(remove.Select(x => x.Id));
+            if (add != null)
+                roleIds = roleIds.Concat(add.Select(x => x.Id));
+            await user.ModifyAsync(x => x.RoleIds = roleIds.ToArray()).ConfigureAwait(false);
+        }
     }
 }