misc: Use '??=' (rebased) (#1391)

Co-authored-by: Christopher Felegy <cfelegy@riseup.net>

Discord.Net.targets

@@ -2,6 +2,7 @@
     <PropertyGroup>
         <VersionPrefix>2.3.0</VersionPrefix>
         <VersionSuffix>dev</VersionSuffix>
+        <LangVersion>latest</LangVersion>
         <Authors>Discord.Net Contributors</Authors>
         <PackageTags>discord;discordapp</PackageTags>
         <PackageProjectUrl>https://github.com/RogueException/Discord.Net</PackageProjectUrl>

src/Discord.Net.Core/Utils/Comparers.cs

@@ -8,27 +8,26 @@ namespace Discord
     /// </summary>
     public static class DiscordComparers
     {
-        // TODO: simplify with '??=' slated for C# 8.0
         /// <summary>
         ///     Gets an <see cref="IEqualityComparer{T}"/> to be used to compare users.
         /// </summary>
-        public static IEqualityComparer<IUser> UserComparer => _userComparer ?? (_userComparer = new EntityEqualityComparer<IUser, ulong>());
+        public static IEqualityComparer<IUser> UserComparer => _userComparer ??= new EntityEqualityComparer<IUser, ulong>();
         /// <summary>
         ///     Gets an <see cref="IEqualityComparer{T}"/> to be used to compare guilds.
         /// </summary>
-        public static IEqualityComparer<IGuild> GuildComparer => _guildComparer ?? (_guildComparer = new EntityEqualityComparer<IGuild, ulong>());
+        public static IEqualityComparer<IGuild> GuildComparer => _guildComparer ??= new EntityEqualityComparer<IGuild, ulong>();
         /// <summary>
         ///     Gets an <see cref="IEqualityComparer{T}"/> to be used to compare channels.
         /// </summary>
-        public static IEqualityComparer<IChannel> ChannelComparer => _channelComparer ?? (_channelComparer = new EntityEqualityComparer<IChannel, ulong>());
+        public static IEqualityComparer<IChannel> ChannelComparer => _channelComparer ??= new EntityEqualityComparer<IChannel, ulong>();
         /// <summary>
         ///     Gets an <see cref="IEqualityComparer{T}"/> to be used to compare roles.
         /// </summary>
-        public static IEqualityComparer<IRole> RoleComparer => _roleComparer ?? (_roleComparer = new EntityEqualityComparer<IRole, ulong>());
+        public static IEqualityComparer<IRole> RoleComparer => _roleComparer ??= new EntityEqualityComparer<IRole, ulong>();
         /// <summary>
         ///     Gets an <see cref="IEqualityComparer{T}"/> to be used to compare messages.
         /// </summary>
-        public static IEqualityComparer<IMessage> MessageComparer => _messageComparer ?? (_messageComparer = new EntityEqualityComparer<IMessage, ulong>());
+        public static IEqualityComparer<IMessage> MessageComparer => _messageComparer ??= new EntityEqualityComparer<IMessage, ulong>();
 
         private static IEqualityComparer<IUser> _userComparer;
         private static IEqualityComparer<IGuild> _guildComparer;