Add FailIfAsync

ErrorOr.sln.DotSettings.user

@@ -0,0 +1,6 @@
+<wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
+	<s:String x:Key="/Default/Environment/UnitTesting/UnitTestSessionStore/Sessions/=808fb239_002D9877_002D47f2_002Db974_002Dc82d7619c531/@EntryIndexedValue">&lt;SessionState ContinuousTestingMode="0" IsActive="True" Name="FailIfAsyncTests" xmlns="urn:schemas-jetbrains-com:jetbrains-ut-session"&gt;&#xD;
+  &lt;TestAncestor&gt;&#xD;
+    &lt;TestId&gt;xUnit::0E84EC69-4E4C-4195-907D-06C96D0140A6::net6.0::Tests.FailIfAsyncTests&lt;/TestId&gt;&#xD;
+  &lt;/TestAncestor&gt;&#xD;
+&lt;/SessionState&gt;</s:String></wpf:ResourceDictionary>

src/ErrorOr.FailIf.cs

@@ -20,4 +20,20 @@ public ErrorOr<TValue> FailIf(Func<TValue, bool> onValue, Error error)
 
         return onValue(Value) ? error : this;
     }
+
+    /// <summary>
+    /// If the state is error, the provider <paramref name="onValue"/> is invoked asynchronously.
+    /// </summary>
+    /// <param name="onValue">The function to execute if the statement is value.</param>
+    /// <param name="error">The <see cref="Error"/> to return if the given <paramref name="onValue"/> function returned true.</param>
+    /// <returns>The given <paramref name="error"/> if <paramref name="onValue"/> returns true; otherwise, the original <see cref="ErrorOr"/> instance.</returns>
+    public async Task<ErrorOr<TValue>> FailIfAsync(Func<TValue, Task<bool>> onValue, Error error)
+    {
+        if (IsError)
+        {
+            return this;
+        }
+
+        return await onValue(Value).ConfigureAwait(false) ? error : this;
+    }
 }

src/ErrorOr.FailIfExtensions.cs

@@ -0,0 +1,5 @@
+namespace ErrorOr;
+
+public static partial class ErrorOrfExtensions
+{
+}

tests/ErrorOr.FailIfAsyncTests.cs

@@ -0,0 +1,54 @@
+using ErrorOr;
+using FluentAssertions;
+
+namespace Tests;
+
+public class FailIfAsyncTests
+{
+    private record Person(string Name);
+
+    [Fact]
+    public async Task CallingFailIfAsync_WhenFailIf_ShouldReturnError()
+    {
+        // Arrange
+        ErrorOr<int> errorOrInt = 5;
+
+        // Act
+        ErrorOr<int> result = await errorOrInt
+            .FailIfAsync(num => Task.FromResult(num > 3), Error.Failure());
+
+        // Assert
+        result.IsError.Should().BeTrue();
+        result.FirstError.Type.Should().Be(ErrorType.Failure);
+    }
+
+    [Fact]
+    public async Task CallingFailIfAsync_WhenFailIf_ShouldReturnValue()
+    {
+        // Arrange
+        ErrorOr<int> errorOrInt = 5;
+
+        // Act
+        ErrorOr<int> result = await errorOrInt
+            .FailIfAsync(num => Task.FromResult(num > 10), Error.Failure());
+
+        // Assert
+        result.IsError.Should().BeFalse();
+        result.Value.Should().Be(5);
+    }
+
+    [Fact]
+    public async Task CallingFailIf_WhenIsError_ShouldNotInvoke_FailIfFunc()
+    {
+        // Arrange
+        ErrorOr<string> errorOrString = Error.NotFound();
+
+        // Act
+        ErrorOr<string> result = await errorOrString
+            .FailIfAsync(str => Task.FromResult(str == string.Empty), Error.Failure());
+
+        // Assert
+        result.IsError.Should().BeTrue();
+        result.FirstError.Type.Should().Be(ErrorType.NotFound);
+    }
+}