Fixed task support

Author: sakno

src/DotNext.Metaprogramming/Threading/Tasks/CompletedTask.cs

@@ -54,12 +54,12 @@ internal readonly struct CompletedTask<T>
     /// </summary>
     /// <param name="task">Completed task.</param>
     public static implicit operator Task<T>(CompletedTask<T> task)
-        => task.result.AsTask();
+        => task.result.AsTask().AsTask();
 
     /// <summary>
     /// Obtains <see cref="ValueTask{TResult}"/> completed synchronously.
     /// </summary>
     /// <param name="task">Completed task.</param>
     public static implicit operator ValueTask<T>(CompletedTask<T> task)
-        => new(task.result.AsTask());
+        => task.result.AsTask();
 }

src/DotNext.Tests/ResultTests.cs

@@ -230,15 +230,12 @@ private static TResult FromError<TError, TResult>(TError error)
     public static async Task ConvertToTask()
     {
         Result<int> result = 42;
-        var task = (Task<int>)result;
-        Equal(42, await task);
+        Equal(42, await (ValueTask<int>)result);
 
         result = Result.FromException<int>(new OperationCanceledException(new CancellationToken(canceled: true)));
-        task = (Task<int>)result;
-        True(task.IsCanceled);
+        True(result.AsTask().IsCanceled);
 
         result = Result.FromException<int>(new Exception());
-        task = (Task<int>)result;
-        await ThrowsAsync<Exception>(Func.Constant(task));
+        await ThrowsAsync<Exception>(result.AsTask().AsTask);
     }
 }

src/DotNext/Result.cs

@@ -319,20 +319,20 @@ public unsafe T OrInvoke(delegate*<Exception, T> defaultFunc)
     /// Converts this result to <see cref="Task{TResult}"/>.
     /// </summary>
     /// <returns>The completed task representing the result.</returns>
-    public Task<T> AsTask()
+    public ValueTask<T> AsTask()
         => exception?.SourceException switch
         {
-            null => Task.FromResult(value),
-            OperationCanceledException canceledEx => Task.FromCanceled<T>(canceledEx.CancellationToken),
-            { } error => Task.FromException<T>(error),
+            null => new(value),
+            OperationCanceledException canceledEx => ValueTask.FromCanceled<T>(canceledEx.CancellationToken),
+            { } error => ValueTask.FromException<T>(error),
         };
 
     /// <summary>
     /// Converts the result to <see cref="Task{TResult}"/>.
     /// </summary>
     /// <param name="result">The result to be converted.</param>
     /// <returns>The completed task representing the result.</returns>
-    public static explicit operator Task<T>(in Result<T> result) => result.AsTask();
+    public static explicit operator ValueTask<T>(in Result<T> result) => result.AsTask();
 
     /// <summary>
     /// Gets boxed representation of the result.