error tests expansion

Railway/Result.cs

@@ -64,7 +64,7 @@ public readonly partial struct Result : IEquatable<Result>
     public static implicit operator Result(Error error) => new(error ?? throw new ArgumentNullException(nameof(error)));
     [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static implicit operator Result(Exception exception) => new(
-        new ExceptionalError(exception ?? throw new ArgumentNullException(nameof(exception))));
+        Error.New(exception ?? throw new ArgumentNullException(nameof(exception))));
     [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static implicit operator Result<SuccessUnit>(Result result) => result.State switch
     {
@@ -75,8 +75,8 @@ public readonly partial struct Result : IEquatable<Result>
     [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static explicit operator Result(SuccessUnit _) => new(null);
 
-    [Pure] public bool IsSuccess => Error is null;
-    [Pure] public bool IsFailure => Error is not null;
+    [Pure] public bool IsSuccess => State == ResultState.Success;
+    [Pure] public bool IsFailure => State == ResultState.Error;
 
     [Pure] public bool TryGetValue([MaybeNullWhen(false)]out SuccessUnit? u, [MaybeNullWhen(true), NotNullWhen(false)]out Error? error)
     {
@@ -236,7 +236,7 @@ public readonly struct Result<T> : IEquatable<Result<T>>
                 if (typeof(R).IsAssignableFrom(typeof(T)) && Value is null)
                     return default(R)!;
 
-                return (R)(object)Value!;
+                return (R)(object)Value!; // throws InvalidCastException by design. should not use cast on incompatible types
             }
 
             default: throw new ResultNotInitializedException();