Add cache purging methods

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

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -15,7 +15,7 @@ namespace Discord
         //public static IReadOnlyCollection<TValue> ToReadOnlyCollection<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> source)
         //    => new CollectionWrapper<TValue>(source.Select(x => x.Value), () => source.Count);
         public static IReadOnlyCollection<TValue> ToReadOnlyCollection<TKey, TValue>(this IDictionary<TKey, TValue> source)
-            => new CollectionWrapper<TValue>(source.Select(x => x.Value), () => source.Count);
+            => new CollectionWrapper<TValue>(source.Values, () => source.Count);
         public static IReadOnlyCollection<TValue> ToReadOnlyCollection<TValue, TSource>(this IEnumerable<TValue> query, IReadOnlyCollection<TSource> source)
             => new CollectionWrapper<TValue>(query, () => source.Count);
         public static IReadOnlyCollection<TValue> ToReadOnlyCollection<TValue>(this IEnumerable<TValue> query, Func<int> countFunc)

src/Discord.Net.WebSocket/ClientState.cs

@@ -82,6 +82,20 @@ namespace Discord.WebSocket
             }
             return null;
         }
+        internal void PurgeAllChannels()
+        {
+            foreach (var guild in _guilds.Values)
+                guild.PurgeChannelCache(this);
+
+            PurgeDMChannels();
+        }
+        internal void PurgeDMChannels()
+        {
+            foreach (var channel in _dmChannels.Values)
+                _channels.TryRemove(channel.Id, out _);
+
+            _dmChannels.Clear();
+        }
 
         internal SocketGuild GetGuild(ulong id)
         {
@@ -96,7 +110,11 @@ namespace Discord.WebSocket
         internal SocketGuild RemoveGuild(ulong id)
         {
             if (_guilds.TryRemove(id, out SocketGuild guild))
+            {
+                guild.PurgeChannelCache(this);
+                guild.PurgeGuildUserCache();
                 return guild;
+            }
             return null;
         }
 
@@ -116,5 +134,10 @@ namespace Discord.WebSocket
                 return user;
             return null;
         }
+        internal void PurgeUsers()
+        {
+            foreach (var guild in _guilds.Values)
+                guild.PurgeGuildUserCache();
+        }
     }
 }

src/Discord.Net.WebSocket/DiscordSocketClient.cs

@@ -306,6 +306,14 @@ namespace Discord.WebSocket
         /// <inheritdoc />
         public override SocketChannel GetChannel(ulong id)
             => State.GetChannel(id);
+        /// <summary>
+        ///     Clears all cached channels from the client.
+        /// </summary>
+        public void PurgeChannelCache() => State.PurgeAllChannels();
+        /// <summary>
+        ///     Clears cached DM channels from the client.
+        /// </summary>
+        public void PurgeDMChannelCache() => State.PurgeDMChannels();
 
         /// <inheritdoc />
         public override SocketUser GetUser(ulong id)
@@ -313,6 +321,10 @@ namespace Discord.WebSocket
         /// <inheritdoc />
         public override SocketUser GetUser(string username, string discriminator)
             => State.Users.FirstOrDefault(x => x.Discriminator == discriminator && x.Username == username);
+        /// <summary>
+        ///     Clears cached users from the client.
+        /// </summary>
+        public void PurgeUserCache() => State.PurgeUsers();
         internal SocketGlobalUser GetOrCreateUser(ClientState state, Discord.API.User model)
         {
             return state.GetOrAddUser(model.Id, x =>

src/Discord.Net.WebSocket/Entities/Guilds/SocketGuild.cs

@@ -623,6 +623,13 @@ namespace Discord.WebSocket
                 return state.RemoveChannel(id) as SocketGuildChannel;
             return null;
         }
+        internal void PurgeChannelCache(ClientState state)
+        {
+            foreach (var channelId in _channels)
+                state.RemoveChannel(channelId);
+
+            _channels.Clear();
+        }
 
         //Voice Regions
         /// <summary>
@@ -797,6 +804,21 @@ namespace Discord.WebSocket
             }
             return null;
         }
+        internal void PurgeGuildUserCache()
+        {
+            var members = Users;
+            var self = CurrentUser;
+            _members.Clear();
+            _members.TryAdd(self.Id, self);
+
+            DownloadedMemberCount = _members.Count;
+
+            foreach (var member in members)
+            {
+                if (member.Id != self.Id)
+                    member.GlobalUser.RemoveRef(Discord);
+            }
+        }
 
         /// <inheritdoc />
         public async Task DownloadUsersAsync()