feature(Result): add mechanism to replace a previous success with Unit

Author: daht-x

Directory.Packages.props

@@ -5,8 +5,8 @@
 	<ItemGroup>
 		<PackageVersion Include="SonarAnalyzer.CSharp" Version="10.4.0.108396" PrivateAssets="all" />
 		<PackageVersion Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="all" />
-		<PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
-		<PackageVersion Include="xunit" Version="2.9.2" />
+		<PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.12.0" PrivateAssets="all" />
+		<PackageVersion Include="xunit" Version="2.9.2" PrivateAssets="all" />
 		<PackageVersion Include="xunit.runner.visualstudio" Version="3.0.0" PrivateAssets="all" />
 		<PackageVersion Include="coverlet.msbuild" Version="6.0.2" PrivateAssets="all" />
 	</ItemGroup>

libraries/core/documentation/monads/result.md

@@ -40,6 +40,7 @@ Type intended to handle both the possible failure and the expected success of a
    - [`Map<TSuccessToMap>(createSuccessToMap)`](#maptsuccesstomapcreatesuccesstomap)
    - [`Bind<TSuccessToBind>(createResultToBind)`](#bindtsuccesstobindcreateresulttobind)
    - [`Reset<TSuccessToInitialize>(initializerResult)`](#resettsuccesstoinitializeinitializerresult)
+   - [`Discard()`](#discard)
    - [`Reduce<TReducer>(reduceFailure, reduceSuccess)`](#reducetreducerreducefailure-reducesuccess)
    - [`Equals(obj)`](#equalsobj)
    - [`Equals(other)`](#equalsother)
@@ -495,6 +496,18 @@ which may have the same or different type of expected success.
 
 ***[Top](#resulttfailure-tsuccess)***
 
+#### `Discard()`
+
+- Signature:
+
+  ```cs
+  public Result<TFailure, Unit> Discard()
+  ```
+
+- Description: Replaces the previous success with [`Unit`](../unit.md).
+
+***[Top](#resulttfailure-tsuccess)***
+
 #### `Reduce<TReducer>(reduceFailure, reduceSuccess)`
 
 - Signature:

libraries/core/source/Monads/Result.cs

@@ -243,6 +243,13 @@ public Result<TFailure, TSuccessInitializer> Reset<TSuccessInitializer>(
 			? new(Failure)
 			: initializerResult;
 
+	/// <summary>Replaces the previous success with <see cref="Unit"/>.</summary>
+	/// <returns>A new failed result if <see cref="IsFailed"/> is <see langword="true" />; otherwise, a new success result containing <see cref="Unit"/>.</returns>
+	public Result<TFailure, Unit> Discard()
+		=> IsFailed
+			? new(Failure)
+			: new(Unit.Discarder);
+
 	/// <summary>Creates a new reduced failure if the previous result is failed; otherwise, creates a new reduced success.</summary>
 	/// <param name="reduceFailure">Creates a possible reduced failure.</param>
 	/// <param name="reduceSuccess">Creates an expected reduced success.</param>

libraries/core/tests/unit/Monads/ResultTests.cs

@@ -24,6 +24,8 @@ public sealed class ResultTests
 
 	private const string memberBind = nameof(Result<object, object>.Bind);
 
+	private const string memberDiscard = nameof(Result<object, object>.Discard);
+
 	private const string memberReduce = nameof(Result<object, object>.Reduce);
 
 	private const string memberEquals = nameof(Result<object, object>.Equals);
@@ -676,6 +678,30 @@ public void Bind_SuccessfulResultPlusCreateResultToBindWithSuccessfulResult_Succ
 
 	#endregion
 
+	#region Discard
+
+	[Fact]
+	[Trait(@base, memberDiscard)]
+	public void Discard_FailedResult_FailedResult()
+	{
+		const string expected = ResultFixture.Failure;
+		Result<string, Unit> actual = ResultMother.Fail(expected)
+			.Discard();
+		ResultAsserter.CheckIfAreFailed(expected, actual);
+	}
+
+	[Fact]
+	[Trait(@base, memberDiscard)]
+	public void Discard_SuccessfulResult_Unit()
+	{
+		Unit expected = Unit.Discarder;
+		Result<string, Unit> actual = ResultMother.Succeed(ResultFixture.Success)
+			.Discard();
+		ResultAsserter.CheckIfAreSuccessful(expected, actual);
+	}
+
+	#endregion
+
 	#region Reduce
 
 	[Fact]