Revert PreconditionResult -> IResult in return types - Change PreconditionResult to a class that PreconditionGroupResult inherits.

src/Discord.Net.Commands/CommandMatch.cs

@@ -16,9 +16,9 @@ namespace Discord.Commands
             Alias = alias;
         }
 
-        public Task<IResult> CheckPreconditionsAsync(ICommandContext context, IServiceProvider services = null)
+        public Task<PreconditionResult> CheckPreconditionsAsync(ICommandContext context, IServiceProvider services = null)
             => Command.CheckPreconditionsAsync(context, services);
-        public Task<ParseResult> ParseAsync(ICommandContext context, SearchResult searchResult, IResult preconditionResult = null)
+        public Task<ParseResult> ParseAsync(ICommandContext context, SearchResult searchResult, PreconditionResult preconditionResult = null)
             => Command.ParseAsync(context, Alias.Length, searchResult, preconditionResult);
         public Task<ExecuteResult> ExecuteAsync(ICommandContext context, IEnumerable<object> argList, IEnumerable<object> paramList, IServiceProvider services)
             => Command.ExecuteAsync(context, argList, paramList, services);

src/Discord.Net.Commands/Info/CommandInfo.cs

@@ -64,7 +64,7 @@ namespace Discord.Commands
             _action = builder.Callback;
         }
 
-        public async Task<IResult> CheckPreconditionsAsync(ICommandContext context, IServiceProvider services = null)
+        public async Task<PreconditionResult> CheckPreconditionsAsync(ICommandContext context, IServiceProvider services = null)
         {
             services = services ?? EmptyServiceProvider.Instance;
 
@@ -105,7 +105,7 @@ namespace Discord.Commands
             return PreconditionResult.FromSuccess();
         }
         
-        public async Task<ParseResult> ParseAsync(ICommandContext context, int startIndex, SearchResult searchResult, IResult preconditionResult = null)
+        public async Task<ParseResult> ParseAsync(ICommandContext context, int startIndex, SearchResult searchResult, PreconditionResult preconditionResult = null)
         {
             if (!searchResult.IsSuccess)
                 return ParseResult.FromError(searchResult);

src/Discord.Net.Commands/Results/PreconditionGroupResult.cs

@@ -5,28 +5,21 @@ using System.Linq;
 namespace Discord.Commands
 {
     [DebuggerDisplay(@"{DebuggerDisplay,nq}")]
-    public struct PreconditionGroupResult : IResult
+    public class PreconditionGroupResult : PreconditionResult
     {
-        public CommandError? Error { get; }
-
-        public string ErrorReason { get; }
-
-        public bool IsSuccess => !Error.HasValue;
-
         public IReadOnlyCollection<PreconditionResult> Preconditions { get; }
 
-        private PreconditionGroupResult(CommandError? error, string errorReason, ICollection<PreconditionResult> preconditions)
+        protected PreconditionGroupResult(CommandError? error, string errorReason, ICollection<PreconditionResult> preconditions)
+            : base(error, errorReason)
         {
-            Error = error;
-            ErrorReason = errorReason;
             Preconditions = (preconditions ?? Enumerable.Empty<PreconditionResult>().ToList()).ToReadOnlyCollection();
         }
 
-        public static PreconditionGroupResult FromSuccess()
+        public static new PreconditionGroupResult FromSuccess()
             => new PreconditionGroupResult(null, null, null);
         public static PreconditionGroupResult FromError(string reason, ICollection<PreconditionResult> preconditions)
             => new PreconditionGroupResult(CommandError.UnmetPrecondition, reason, preconditions);
-        public static PreconditionGroupResult FromError(IResult result) //needed?
+        public static new PreconditionGroupResult FromError(IResult result) //needed?
             => new PreconditionGroupResult(result.Error, result.ErrorReason, null);
 
         public override string ToString() => IsSuccess ? "Success" : $"{Error}: {ErrorReason}";

src/Discord.Net.Commands/Results/PreconditionResult.cs

@@ -3,14 +3,14 @@
 namespace Discord.Commands
 {
     [DebuggerDisplay(@"{DebuggerDisplay,nq}")]
-    public struct PreconditionResult : IResult
+    public class PreconditionResult : IResult
     {
         public CommandError? Error { get; }
         public string ErrorReason { get; }
 
         public bool IsSuccess => !Error.HasValue;
 
-        private PreconditionResult(CommandError? error, string errorReason)
+        protected PreconditionResult(CommandError? error, string errorReason)
         {
             Error = error;
             ErrorReason = errorReason;