Ch4PizzaStore: last part with AbstractFactory. This example in the book is really TERRIBLE.

Ch4PizzaStore/Ch4PizzaStore.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net9.0</TargetFramework>
+        <LangVersion>latestmajor</LangVersion>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+</Project>

Ch4PizzaStore/Pizza.cs

@@ -0,0 +1,139 @@
+namespace Ch4PizzaStore;
+
+public abstract class Pizza(string name) {
+    public string Name { get; internal set; } = name;
+    public IDough? Dough { get; internal set; } = null;
+    public ISauce? Sauce { get; internal set; } = null;
+    public IVeggies[]? VeggiesArray { get; internal set; } = null;
+    public ICheese? Cheese { get; internal set; } = null;
+    public IPepperoni? Pepperoni { get; internal set; } = null;
+    public IClams? Clams { get; internal set; } = null;
+
+    internal abstract void Prepare();
+
+    // While in Java all methods are by default `virtual`, C# is the same as C++,
+    // all methods are final/selaed until explicitly marked as virtual.
+    internal virtual void Bake() {
+        Console.WriteLine("Bake for 25 minutes at 350");
+    }
+
+    internal virtual void Cut() {
+        Console.WriteLine("Cutting the pizza into diagonal slices");
+    }
+
+    internal virtual void Box() {
+        Console.WriteLine("Place pizza in official PizzaStore box");
+    }
+
+    public override string ToString() {
+        return "Pizza!"; // TODO: code to print the pizza here
+    }
+}
+
+public class CheesePizza(IPizzaIngredientFactory ingredientFactory, string name) : Pizza(name) {
+    internal override void Prepare() {
+        Console.WriteLine($"Preparing {Name}");
+        Dough = ingredientFactory.CreateDough();
+        Sauce = ingredientFactory.CreateSauce();
+        Cheese = ingredientFactory.CreateCheese();
+    }
+}
+
+public class ClamPizza(IPizzaIngredientFactory ingredientFactory, string name) : Pizza(name) {
+    internal override void Prepare() {
+        Console.WriteLine($"Preparing {Name}");
+        Dough = ingredientFactory.CreateDough();
+        Sauce = ingredientFactory.CreateSauce();
+        Cheese = ingredientFactory.CreateCheese();
+        Clams = ingredientFactory.CreateClams();
+    }
+}
+
+public abstract class PizzaStore {
+    protected abstract Pizza CreatePizza(string type);
+
+    public Pizza OrderPizza(string type) {
+        var pizza = CreatePizza(type);
+        pizza.Prepare();
+        pizza.Bake();
+        pizza.Cut();
+        pizza.Box();
+        return pizza;
+    }
+}
+
+public class NYPizzaStore : PizzaStore {
+    protected override Pizza CreatePizza(string type) {
+        var ingredientFactory = new NYPizzaIngredientFactory();
+        return type switch {
+            "cheese" => new CheesePizza(ingredientFactory, "New York Style Cheese Pizza"),
+            "clam" => new ClamPizza(ingredientFactory, "New York Style Clam Pizza"),
+            _ => throw new ArgumentOutOfRangeException(nameof(type), type, null)
+        };
+    }
+}
+
+public interface IDough;
+
+public interface ISauce;
+
+public interface ICheese;
+
+public interface IVeggies;
+
+public interface IPepperoni;
+
+public interface IClams;
+
+public interface IPizzaIngredientFactory {
+    public IDough CreateDough();
+    public ISauce CreateSauce();
+    public ICheese CreateCheese();
+    public IVeggies[] CreateVeggies();
+    public IPepperoni CreatePepperoni();
+    public IClams CreateClams();
+}
+
+public class ThinCrustDough : IDough;
+
+public class MarinaraSauce : ISauce;
+
+public class ReggianoCheese : ICheese;
+
+public class Garlic : IVeggies;
+
+public class Onion : IVeggies;
+
+public class Mushroom : IVeggies;
+
+public class RedPepper : IVeggies;
+
+public class SlicedPepperoni : IPepperoni;
+
+public class FreshClams : IClams;
+
+public class NYPizzaIngredientFactory : IPizzaIngredientFactory {
+    public IDough CreateDough() {
+        return new ThinCrustDough();
+    }
+
+    public ISauce CreateSauce() {
+        return new MarinaraSauce();
+    }
+
+    public ICheese CreateCheese() {
+        return new ReggianoCheese();
+    }
+
+    public IVeggies[] CreateVeggies() {
+        return [new Garlic(), new Onion(), new Mushroom(), new RedPepper()];
+    }
+
+    public IPepperoni CreatePepperoni() {
+        return new SlicedPepperoni();
+    }
+
+    public IClams CreateClams() {
+        return new FreshClams();
+    }
+}

Ch4PizzaStore/Program.cs

@@ -0,0 +1,10 @@
+// See https://aka.ms/new-console-template for more information
+
+using Ch4PizzaStore;
+
+PizzaStore nyStore = new NYPizzaStore();
+
+var pizza = nyStore.OrderPizza("cheese");
+Console.WriteLine($"Ethan ordered a {pizza.Name}\n");
+pizza = nyStore.OrderPizza("clam");
+Console.WriteLine($"Joel ordered a {pizza.Name}\n");

HeadFirstDesignPatterns.sln

@@ -6,6 +6,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ch2Weather", "Ch2Weather\Ch
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ch3Beverage", "Ch3Beverage\Ch3Beverage.csproj", "{8F380143-DDBC-4785-B4F2-7B32EBE54515}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ch4PizzaStore", "Ch4PizzaStore\Ch4PizzaStore.csproj", "{EECD03A1-DE37-4E1B-8487-0A6DE21FBDB3}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -24,5 +26,9 @@ Global
 		{8F380143-DDBC-4785-B4F2-7B32EBE54515}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{8F380143-DDBC-4785-B4F2-7B32EBE54515}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{8F380143-DDBC-4785-B4F2-7B32EBE54515}.Release|Any CPU.Build.0 = Release|Any CPU
+		{EECD03A1-DE37-4E1B-8487-0A6DE21FBDB3}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{EECD03A1-DE37-4E1B-8487-0A6DE21FBDB3}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{EECD03A1-DE37-4E1B-8487-0A6DE21FBDB3}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{EECD03A1-DE37-4E1B-8487-0A6DE21FBDB3}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 EndGlobal

HeadFirstDesignPatterns.sln.DotSettings

@@ -0,0 +1,2 @@
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+	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/Abbreviations/=NY/@EntryIndexedValue">NY</s:String></wpf:ResourceDictionary>