From 6052982b84c9500d8f0571b6ce25d6b37f9bbb78 Mon Sep 17 00:00:00 2001
From: Mitch Lienau <mitch@feature23.com>
Date: Mon, 1 Dec 2025 10:16:07 -0500
Subject: [PATCH] #16 - Preserve PreconditionFailed message when mapping to
 other type

---
 .../Results/PreconditionFailedResultTests.cs  | 23 +++++++++++++++++++
 src/F23.Kernel/Result.cs                      |  2 +-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/F23.Kernel.Tests/Results/PreconditionFailedResultTests.cs b/src/F23.Kernel.Tests/Results/PreconditionFailedResultTests.cs
index 2af30da..645b6c0 100644
--- a/src/F23.Kernel.Tests/Results/PreconditionFailedResultTests.cs
+++ b/src/F23.Kernel.Tests/Results/PreconditionFailedResultTests.cs
@@ -15,5 +15,28 @@ public void PreconditionFailedResult_SuccessIsFalse(PreconditionFailedReason rea
 
         // Assert
         Assert.False(result.IsSuccess);
+    }
+
+    [Theory]
+    [InlineData(PreconditionFailedReason.NotFound)]
+    [InlineData(PreconditionFailedReason.ConcurrencyMismatch)]
+    [InlineData(PreconditionFailedReason.Conflict)]
+    public void MappingPreconditionFailedResultToOther_PreservesTheReasonAndMessage(PreconditionFailedReason reason)
+    {
+        // Arrange
+        var originalMessage = "Original failure message";
+        var originalResult = new PreconditionFailedResult<Original>(reason, originalMessage);
+
+        // Act
+        var mappedResult = originalResult.MapFailure<Other>();
+
+        // Assert
+        var preconditionFailedResult = Assert.IsType<PreconditionFailedResult<Other>>(mappedResult);
+        Assert.Equal(reason, preconditionFailedResult.Reason);
+        Assert.Equal(originalMessage, preconditionFailedResult.Message);
     }
+
+    private class Original { }
+
+    private class Other { }
 }
diff --git a/src/F23.Kernel/Result.cs b/src/F23.Kernel/Result.cs
index dbddb18..90f247d 100644
--- a/src/F23.Kernel/Result.cs
+++ b/src/F23.Kernel/Result.cs
@@ -151,7 +151,7 @@ public Result<TOther> MapFailure<TOther>() =>
             SuccessResult<T> => throw new InvalidOperationException("Cannot map failure on success result"),
             ValidationFailedResult<T> validationFailed => Result<TOther>.ValidationFailed(validationFailed.Errors),
             UnauthorizedResult<T> unauthorized => Result<TOther>.Unauthorized(unauthorized.Message),
-            PreconditionFailedResult<T> preconditionFailed => Result<TOther>.PreconditionFailed(preconditionFailed.Reason),
+            PreconditionFailedResult<T> preconditionFailed => Result<TOther>.PreconditionFailed(preconditionFailed.Reason, preconditionFailed.Message),
             _ => throw new InvalidOperationException("Unknown result type")
         };