From e96f6ec579d1b76f7bbbee4cb227e61bff10ed75 Mon Sep 17 00:00:00 2001
From: Vladimir Pecanac <vladimir.pecanac@gmail.com>
Date: Sun, 18 Oct 2026 00:04:27 +0200
Subject: [PATCH] Readonly Modifier in C#: retarget net10.0, Playlist,
 Counter/Tally trap, Book init property, three tests

Both projects net7.0 to net10.0. Microsoft.NET.Test.Sdk 18.11.0, xunit 2.9.3, xunit.runner.visualstudio 4.0.1, coverlet.collector 10.1.0. New Playlist (a readonly List<string> field that still accepts items; the reassignment in Reset() stays commented out as a compiler error), Counter (a mutable struct with a readonly Describe() method), Tally (a readonly Counter field whose Increment() calls run on a defensive copy, so Total stays 0) and Book (required init-only Title). Program.cs prints each one. Three new tests: the readonly list changes, the readonly struct field total stays 0, and a Counter variable increments to 2. Existing files and tests unchanged.
---
 .../ReadOnlyModifierInCSharp/Book.cs          |  7 ++++
 .../ReadOnlyModifierInCSharp/Counter.cs       | 17 ++++++++++
 .../ReadOnlyModifierInCSharp/Playlist.cs      | 19 +++++++++++
 .../ReadOnlyModifierInCSharp/Program.cs       | 22 ++++++++++++-
 .../ReadOnlyModifierInCSharp.csproj           |  2 +-
 .../ReadOnlyModifierInCSharp/Tally.cs         | 14 ++++++++
 .../ReadOnlyTests/ReadOnlyTests.cs            | 32 ++++++++++++++++++-
 .../ReadOnlyTests/ReadOnlyTests.csproj        | 10 +++---
 8 files changed, 115 insertions(+), 8 deletions(-)
 create mode 100644 csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Book.cs
 create mode 100644 csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Counter.cs
 create mode 100644 csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Playlist.cs
 create mode 100644 csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Tally.cs

diff --git a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Book.cs b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Book.cs
new file mode 100644
index 0000000000..820e655fc1
--- /dev/null
+++ b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Book.cs
@@ -0,0 +1,7 @@
+namespace ReadOnlyModifierInCSharp
+{
+    public class Book
+    {
+        public required string Title { get; init; }
+    }
+}
diff --git a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Counter.cs b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Counter.cs
new file mode 100644
index 0000000000..a169914300
--- /dev/null
+++ b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Counter.cs
@@ -0,0 +1,17 @@
+namespace ReadOnlyModifierInCSharp
+{
+    public struct Counter
+    {
+        public int Value { get; private set; }
+
+        public void Increment()
+        {
+            Value++;
+        }
+
+        public readonly string Describe()
+        {
+            return $"Counted {Value} times";
+        }
+    }
+}
diff --git a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Playlist.cs b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Playlist.cs
new file mode 100644
index 0000000000..4fe0eae17b
--- /dev/null
+++ b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Playlist.cs
@@ -0,0 +1,19 @@
+namespace ReadOnlyModifierInCSharp
+{
+    public class Playlist
+    {
+        private readonly List<string> _songs = new();
+
+        public int Count => _songs.Count;
+
+        public void Add(string song)
+        {
+            _songs.Add(song);
+        }
+
+        public void Reset()
+        {
+            //_songs = new List<string>(); //Throws Compiler Error
+        }
+    }
+}
diff --git a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Program.cs b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Program.cs
index f1843e1800..b37261d19e 100644
--- a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Program.cs
+++ b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Program.cs
@@ -18,4 +18,24 @@
 //person.Name = "Emily"; //Throws compiler error
 
 person.ChangeName("Emily");
-Console.WriteLine($"Changed Name: {person.Name}");
\ No newline at end of file
+Console.WriteLine($"Changed Name: {person.Name}");
+
+var playlist = new Playlist();
+playlist.Add("Bohemian Rhapsody");
+playlist.Add("Hotel California");
+Console.WriteLine($"Songs: {playlist.Count}");
+
+var tally = new Tally();
+tally.Count();
+tally.Count();
+Console.WriteLine($"Total: {tally.Total}");
+
+var counter = new Counter();
+counter.Increment();
+counter.Increment();
+Console.WriteLine(counter.Describe());
+
+var book = new Book { Title = "Dune" };
+Console.WriteLine($"Title: {book.Title}");
+
+//book.Title = "Emma"; //Throws compiler error
diff --git a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp.csproj b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp.csproj
index f02677bf64..dfb40caafc 100644
--- a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp.csproj
+++ b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>
diff --git a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Tally.cs b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Tally.cs
new file mode 100644
index 0000000000..436708900b
--- /dev/null
+++ b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyModifierInCSharp/Tally.cs
@@ -0,0 +1,14 @@
+namespace ReadOnlyModifierInCSharp
+{
+    public class Tally
+    {
+        private readonly Counter _counter;
+
+        public int Total => _counter.Value;
+
+        public void Count()
+        {
+            _counter.Increment();
+        }
+    }
+}
diff --git a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyTests/ReadOnlyTests.cs b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyTests/ReadOnlyTests.cs
index bdb7c4da7d..977555c6df 100644
--- a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyTests/ReadOnlyTests.cs
+++ b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyTests/ReadOnlyTests.cs
@@ -20,4 +20,34 @@ public void GivenPerson_WhenCallingChangeName_ThenNameChanged()
 
         Assert.Equal(expectedName, person.Name);
     }
-}
\ No newline at end of file
+
+    [Fact]
+    public void GivenReadonlyListField_WhenAddingSongs_ThenListChanges()
+    {
+        var playlist = new Playlist();
+        playlist.Add("Bohemian Rhapsody");
+        playlist.Add("Hotel California");
+
+        Assert.Equal(2, playlist.Count);
+    }
+
+    [Fact]
+    public void GivenReadonlyStructField_WhenCountingTwice_ThenTotalStaysZero()
+    {
+        var tally = new Tally();
+        tally.Count();
+        tally.Count();
+
+        Assert.Equal(0, tally.Total);
+    }
+
+    [Fact]
+    public void GivenCounterVariable_WhenIncrementingTwice_ThenValueIsTwo()
+    {
+        var counter = new Counter();
+        counter.Increment();
+        counter.Increment();
+
+        Assert.Equal("Counted 2 times", counter.Describe());
+    }
+}
diff --git a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyTests/ReadOnlyTests.csproj b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyTests/ReadOnlyTests.csproj
index 2c5f1dc0d0..0c8f91bf24 100644
--- a/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyTests/ReadOnlyTests.csproj
+++ b/csharp-intermediate-topics/ReadOnlyModifierInCSharp/ReadOnlyTests/ReadOnlyTests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
 
@@ -10,13 +10,13 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.5.0" />
-    <PackageReference Include="xunit" Version="2.4.2" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.11.0" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.1">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
-    <PackageReference Include="coverlet.collector" Version="3.2.0">
+    <PackageReference Include="coverlet.collector" Version="10.1.0">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>