Partially fixed #266

Author: sakno

src/DotNext.Tests/ResultTests.cs

@@ -254,4 +254,15 @@ public static void ValueRef()
         result = Result.FromException<int>(new ArithmeticException());
         Throws<ArithmeticException>(() => result.ValueRef);
     }
+
+    [Fact]
+    public static void NonNullResult()
+    {
+        var result = default(Result<string>).EnsureNotNull();
+        False(result.IsSuccessful);
+        Throws<NullReferenceException>(() => result.Value);
+
+        result = Result.FromValue("").EnsureNotNull();
+        True(result.IsSuccessful);
+    }
 }

src/DotNext/Result.cs

@@ -51,7 +51,8 @@ public static class Result
     /// </summary>
     /// <param name="resultType">The type of <see cref="Result{T}"/>.</param>
     /// <returns><see langword="true"/>, if specified type is result type; otherwise, <see langword="false"/>.</returns>
-    public static bool IsResult(this Type resultType) => resultType.IsConstructedGenericType && resultType.GetGenericTypeDefinition().IsOneOf([typeof(Result<>), typeof(Result<,>)]);
+    public static bool IsResult(this Type resultType) => resultType.IsConstructedGenericType &&
+                                                         resultType.GetGenericTypeDefinition().IsOneOf([typeof(Result<>), typeof(Result<,>)]);
 
     /// <summary>
     /// Returns the underlying type argument of the specified result type.
@@ -75,6 +76,30 @@ public static class Result
     /// <param name="e">The exception to be placed to the container.</param>
     /// <returns>The exception encapsulated by <see cref="Result{T}"/>.</returns>
     public static Result<T> FromException<T>(Exception e) => new(e);
+
+    /// <summary>
+    /// Ensures that the specified result doesn't contain null value.
+    /// </summary>
+    /// <param name="result">The result to be checked.</param>
+    /// <typeparam name="T">The type of the result.</typeparam>
+    /// <returns>The result containing non-null value; or <see cref="NullReferenceException"/> as an error.</returns>
+    public static Result<T> EnsureNotNull<T>(this Result<T?> result)
+        where T : class
+        => EnsureNotNull<T, NullReferenceException>(result);
+
+    /// <summary>
+    /// Ensures that the specified result doesn't contain null value.
+    /// </summary>
+    /// <param name="result">The result to be checked.</param>
+    /// <typeparam name="T">The type of the result.</typeparam>
+    /// <typeparam name="TException">The type of the exception to be returned from the null result.</typeparam>
+    /// <returns>The result containing non-null value; or <paramref cref="TException"/> as an error.</returns>
+    public static Result<T> EnsureNotNull<T, TException>(this Result<T?> result)
+        where T : class
+        where TException : Exception, new()
+        => result.IsNull
+            ? FromException<T>(ExceptionDispatchInfo.SetCurrentStackTrace(new TException()))
+            : result!;
 }
 
 /// <summary>
@@ -102,6 +127,10 @@ public Result(Exception error)
     {
     }
 
+    [JsonIgnore]
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    internal bool IsNull => exception is null && value is null;
+
     private Result(ExceptionDispatchInfo dispatchInfo)
     {
         Unsafe.SkipInit(out value);