From cc041b86e44de43a2b64a7bc30e822743e907877 Mon Sep 17 00:00:00 2001
From: Daniel <dan.olvera@intellitect.com>
Date: Mon, 11 Sep 2023 08:57:56 -0700
Subject: [PATCH 1/2] fix: Uncommented listing and added compilerAssert tests

Had to add an extra class that derived from PdaItem. The code now throws the error
---
 src/Chapter12.Tests/Listing12.41.Tests.cs        | 15 +++++++++++++++
 ...1.PreventingCovarianceMaintainsHomogeneity.cs | 16 +++++++++++++---
 2 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 src/Chapter12.Tests/Listing12.41.Tests.cs

diff --git a/src/Chapter12.Tests/Listing12.41.Tests.cs b/src/Chapter12.Tests/Listing12.41.Tests.cs
new file mode 100644
index 000000000..85a1698bb
--- /dev/null
+++ b/src/Chapter12.Tests/Listing12.41.Tests.cs
@@ -0,0 +1,15 @@
+using AddisonWesley.Michaelis.EssentialCSharp.Shared.Tests;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace AddisonWesley.Michaelis.EssentialCSharp.Chapter12.Listing12_41.Tests;
+
+[TestClass]
+public class Listing12
+{
+    [TestMethod]
+    public async Task CannotConvertTypes()
+    {
+        await CompilerAssert.CompileTestTargetFileAsync(
+            new string[] { "CS0030" });
+    }
+}
diff --git a/src/Chapter12/Listing12.41.PreventingCovarianceMaintainsHomogeneity.cs b/src/Chapter12/Listing12.41.PreventingCovarianceMaintainsHomogeneity.cs
index 2d5678588..48354b5ea 100644
--- a/src/Chapter12/Listing12.41.PreventingCovarianceMaintainsHomogeneity.cs
+++ b/src/Chapter12/Listing12.41.PreventingCovarianceMaintainsHomogeneity.cs
@@ -1,4 +1,5 @@
-using AddisonWesley.Michaelis.EssentialCSharp.Chapter08.Listing08_05;
+using AddisonWesley.Michaelis.EssentialCSharp.Chapter08.Listing08_02;
+using AddisonWesley.Michaelis.EssentialCSharp.Chapter12.Listing12_08;
 using AddisonWesley.Michaelis.EssentialCSharp.Chapter12.Listing12_11;
 
 namespace AddisonWesley.Michaelis.EssentialCSharp.Chapter12.Listing12_41;
@@ -14,12 +15,21 @@ public static void Main()
         Pair<Contact> contacts = new(contact1, contact2);
 
         #region HIGHLIGHT
+        #if COMPILEERROR // EXCLUDE
         // This gives an error: Cannot convert type ...
         // But suppose it did not
-        // IPair<PdaItem> pdaPair = (IPair<PdaItem>) contacts;
+        IPair<PdaItem> pdaPair = (IPair<PdaItem>) contacts;
         // This is perfectly legal, but not type-safe
-        // pair.First = new Address("123 Sesame Street");
+        pdaPair.First = new Address("123 Sesame Street");
+        #endif // COMPILEERROR // EXCLUDE
         #endregion HIGHLIGHT
         #endregion INCLUDE
     }
 }
+
+public class Address : PdaItem
+{
+    public Address(string address) : base(address)
+    {
+    }
+}

From 82e75bb3b7f2d20e8ec451bc23402cf64e5c2f5e Mon Sep 17 00:00:00 2001
From: Daniel <dan.olvera@intellitect.com>
Date: Mon, 11 Sep 2023 09:34:07 -0700
Subject: [PATCH 2/2] fix: Had to add classes inline to bypass other errors

---
 ...reventingCovarianceMaintainsHomogeneity.cs | 40 +++++++++++++++++--
 1 file changed, 36 insertions(+), 4 deletions(-)

diff --git a/src/Chapter12/Listing12.41.PreventingCovarianceMaintainsHomogeneity.cs b/src/Chapter12/Listing12.41.PreventingCovarianceMaintainsHomogeneity.cs
index 48354b5ea..83f996371 100644
--- a/src/Chapter12/Listing12.41.PreventingCovarianceMaintainsHomogeneity.cs
+++ b/src/Chapter12/Listing12.41.PreventingCovarianceMaintainsHomogeneity.cs
@@ -1,7 +1,3 @@
-using AddisonWesley.Michaelis.EssentialCSharp.Chapter08.Listing08_02;
-using AddisonWesley.Michaelis.EssentialCSharp.Chapter12.Listing12_08;
-using AddisonWesley.Michaelis.EssentialCSharp.Chapter12.Listing12_11;
-
 namespace AddisonWesley.Michaelis.EssentialCSharp.Chapter12.Listing12_41;
 
 public class Program
@@ -33,3 +29,39 @@ public Address(string address) : base(address)
     {
     }
 }
+
+public struct Pair<T> : IPair<T>
+{
+    public Pair(T first, T second)
+    {
+        First = first;
+        Second = second;
+    }
+
+    public T First { get; set; }
+    public T Second { get; set; }
+}
+
+interface IPair<T>
+{
+    T First { get; set; }
+    T Second { get; set; }
+}
+
+public class Contact : PdaItem
+{
+    public Contact(string name)
+        : base(name)
+    {
+    }
+}
+
+public abstract class PdaItem
+{
+    public PdaItem(string name)
+    {
+        Name = name;
+    }
+
+    public virtual string Name { get; set; }
+}