Update tutorials to .NET 6 (#28404)

* Update to .NET 6

Use the latest .NET 6 template.

Fixes #27896

* Update tutorials to .NET 6

Fixes #27896

Also, in this PR, update all the tutorials in the Get Started and Tutorials section to .NET 6. That includes using top-level statements, implicit usings, and following other conventions.

Because I changed so much of the included code, I updated the date on the associated articles even though the text didn't change as much.

* Apply suggestions from code review

Co-authored-by: David Pine <[email protected]>

* Apply suggestions from code review

* Update docs/csharp/fundamentals/tutorials/snippets/patterns/finished/toll-calculator/Program.cs

Co-authored-by: David Pine <[email protected]>

Author: BillWagner

docs/csharp/fundamentals/tutorials/classes.md

@@ -1,7 +1,7 @@
 ---
 title: Classes and objects  - C# Fundamentals tutorial
 description: Create your first C# program and explore object oriented concepts
-ms.date: 05/14/2021
+ms.date: 02/25/2022
 ---
 # Explore object oriented programming with classes and objects
 
@@ -16,21 +16,11 @@ The tutorial expects that you have a machine set up for local development. On Wi
 Using a terminal window, create a directory named *classes*. You'll build your application there. Change to that directory and type `dotnet new console` in the console window. This command creates your application. Open *Program.cs*. It should look like this:
 
 ```csharp
-using System;
-
-namespace classes
-{
-    class Program
-    {
-        static void Main(string[] args)
-        {
-            Console.WriteLine("Hello World!");
-        }
-    }
-}
+// See https://aka.ms/new-console-template for more information
+Console.WriteLine("Hello, World!");
 ```
 
-In this tutorial, you're going to create new types that represent a bank account. Typically developers define each class in a different text file. That makes it easier to manage as a program grows in size. Create a new file named *BankAccount.cs* in the *classes* directory.
+In this tutorial, you're going to create new types that represent a bank account. Typically developers define each class in a different text file. That makes it easier to manage as a program grows in size. Create a new file named *BankAccount.cs* in the *Classes* directory.
 
 This file will contain the definition of a ***bank account***. Object Oriented programming organizes code by creating types in the form of ***classes***. These classes contain the code that represents a specific entity. The `BankAccount` class represents a bank account. The code implements specific operations through methods and properties. In this tutorial, the bank account supports this behavior:
 
@@ -47,23 +37,20 @@ This file will contain the definition of a ***bank account***. Object Oriented p
 You can start by creating the basics of a class that defines that behavior. Create a new file using the **File:New** command. Name it *BankAccount.cs*. Add the following code to your *BankAccount.cs* file:
 
 ```csharp
-using System;
+namespace Classes;
 
-namespace classes
+public class BankAccount
 {
-    public class BankAccount
-    {
-        public string Number { get; }
-        public string Owner { get; set; }
-        public decimal Balance { get; }
+    public string Number { get; }
+    public string Owner { get; set; }
+    public decimal Balance { get; }
 
-        public void MakeDeposit(decimal amount, DateTime date, string note)
-        {
-        }
+    public void MakeDeposit(decimal amount, DateTime date, string note)
+    {
+    }
 
-        public void MakeWithdrawal(decimal amount, DateTime date, string note)
-        {
-        }
+    public void MakeWithdrawal(decimal amount, DateTime date, string note)
+    {
     }
 }
 ```
@@ -89,6 +76,8 @@ public BankAccount(string name, decimal initialBalance)
 Constructors are called when you create an object using [`new`](../../language-reference/operators/new-operator.md). Replace the line `Console.WriteLine("Hello World!");` in *Program.cs* with the following code (replace `<name>` with your name):
 
 ```csharp
+using Classes;
+
 var account = new BankAccount("<name>", 1000);
 Console.WriteLine($"Account {account.Number} was created for {account.Owner} with {account.Balance} initial balance.");
 ```
@@ -124,12 +113,6 @@ Now, let's add a <xref:System.Collections.Generic.List%601> of `Transaction` obj
 
 :::code language="csharp" source="./snippets/introduction-to-classes/BankAccount.cs" id="TransactionDeclaration":::
 
-The <xref:System.Collections.Generic.List%601> class requires you to import a different namespace. Add the following at the beginning of *BankAccount.cs*:
-
-```csharp
-using System.Collections.Generic;
-```
-
 Now, let's correctly compute the `Balance`. The current balance can be found by summing the values of all transactions. As the code is currently, you can only get the initial balance of the account, so you'll have to update the `Balance` property. Replace the line `public decimal Balance { get; }` in *BankAccount.cs* with the following code:
 
 :::code language="csharp" source="./snippets/introduction-to-classes/BankAccount.cs" id="BalanceComputation":::

docs/csharp/fundamentals/tutorials/how-to-display-command-line-arguments.md

@@ -1,7 +1,7 @@
 ---
 title: "How to display command-line arguments"
 description: Learn how to display command-line arguments. See a code example and view additional available resources.
-ms.date: 03/08/2021
+ms.date: 02/25/2022
 ms.topic: how-to
 helpviewer_keywords: 
   - "command-line arguments [C#], displaying"

docs/csharp/fundamentals/tutorials/inheritance.md

@@ -1,7 +1,7 @@
 ---
 title: Inheritance in C#
 description: Learn to use inheritance in C# libraries and applications.
-ms.date: 07/05/2018
+ms.date: 02/25/2022
 ms.assetid: aeb68c74-0ea0-406f-9fbe-2ce02d47ef31
 ---
 # Inheritance in C# and .NET
@@ -93,8 +93,6 @@ public class B : A // Generates CS0534.
 Inheritance applies only to classes and interfaces. Other type categories (structs, delegates, and enums) do not support inheritance. Because of these rules, attempting to compile code like the following example produces compiler error CS0527: "Type 'ValueType' in interface list is not an interface." The error message indicates that, although you can define the interfaces that a struct implements, inheritance is not supported.
 
 ```csharp
-using System;
-
 public struct ValueStructure : ValueType // Generates CS0527.
 {
 }

docs/csharp/fundamentals/tutorials/oop.md

@@ -1,7 +1,7 @@
 ---
 title: "Object-Oriented Programming (C#)"
 description: C# provides full support for object-oriented programming including abstraction, encapsulation, inheritance, and polymorphism.
-ms.date: 05/14/2021
+ms.date: 02/25/2022
 ---
 # Object-Oriented programming (C#)
 

docs/csharp/fundamentals/tutorials/pattern-matching.md

@@ -1,7 +1,7 @@
 ---
 title: "Tutorial: Build algorithms with pattern matching"
 description: This advanced tutorial demonstrates how to use pattern matching techniques to create functionality using data and algorithms that are created separately.
-ms.date: 10/01/2021
+ms.date: 02/25/2022
 ms.custom: contperf-fy21q1
 ---
 # Tutorial: Use pattern matching to build type-driven and data-driven algorithms
@@ -64,21 +64,20 @@ using CommercialRegistration;
 using ConsumerVehicleRegistration;
 using LiveryRegistration;
 
-namespace toll_calculator
+namespace Calculators;
+
+public class TollCalculator
 {
-    public class TollCalculator
+    public decimal CalculateToll(object vehicle) =>
+        vehicle switch
     {
-        public decimal CalculateToll(object vehicle) =>
-            vehicle switch
-        {
-            Car c           => 2.00m,
-            Taxi t          => 3.50m,
-            Bus b           => 5.00m,
-            DeliveryTruck t => 10.00m,
-            { }             => throw new ArgumentException(message: "Not a known vehicle type", paramName: nameof(vehicle)),
-            null            => throw new ArgumentNullException(nameof(vehicle))
-        };
-    }
+        Car c           => 2.00m,
+        Taxi t          => 3.50m,
+        Bus b           => 5.00m,
+        DeliveryTruck t => 10.00m,
+        { }             => throw new ArgumentException(message: "Not a known vehicle type", paramName: nameof(vehicle)),
+        null            => throw new ArgumentNullException(nameof(vehicle))
+    };
 }
 ```
 
@@ -92,42 +91,35 @@ using CommercialRegistration;
 using ConsumerVehicleRegistration;
 using LiveryRegistration;
 
-namespace toll_calculator
+using toll_calculator;
+
+var tollCalc = new TollCalculator();
+
+var car = new Car();
+var taxi = new Taxi();
+var bus = new Bus();
+var truck = new DeliveryTruck();
+
+Console.WriteLine($"The toll for a car is {tollCalc.CalculateToll(car)}");
+Console.WriteLine($"The toll for a taxi is {tollCalc.CalculateToll(taxi)}");
+Console.WriteLine($"The toll for a bus is {tollCalc.CalculateToll(bus)}");
+Console.WriteLine($"The toll for a truck is {tollCalc.CalculateToll(truck)}");
+
+try
 {
-    class Program
-    {
-        static void Main(string[] args)
-        {
-            var tollCalc = new TollCalculator();
-
-            var car = new Car();
-            var taxi = new Taxi();
-            var bus = new Bus();
-            var truck = new DeliveryTruck();
-
-            Console.WriteLine($"The toll for a car is {tollCalc.CalculateToll(car)}");
-            Console.WriteLine($"The toll for a taxi is {tollCalc.CalculateToll(taxi)}");
-            Console.WriteLine($"The toll for a bus is {tollCalc.CalculateToll(bus)}");
-            Console.WriteLine($"The toll for a truck is {tollCalc.CalculateToll(truck)}");
-
-            try
-            {
-                tollCalc.CalculateToll("this will fail");
-            }
-            catch (ArgumentException e)
-            {
-                Console.WriteLine("Caught an argument exception when using the wrong type");
-            }
-            try
-            {
-                tollCalc.CalculateToll(null!);
-            }
-            catch (ArgumentNullException e)
-            {
-                Console.WriteLine("Caught an argument exception when using null");
-            }
-        }
-    }
+    tollCalc.CalculateToll("this will fail");
+}
+catch (ArgumentException e)
+{
+    Console.WriteLine("Caught an argument exception when using the wrong type");
+}
+try
+{
+    tollCalc.CalculateToll(null!);
+}
+catch (ArgumentNullException e)
+{
+    Console.WriteLine("Caught an argument exception when using null");
 }
 ```
 

docs/csharp/fundamentals/tutorials/safely-cast-using-pattern-matching-is-and-as-operators.md

@@ -1,7 +1,7 @@
 ---
 title: "How to safely cast by using pattern matching and the is and as operators"
 description: Learn to use pattern matching techniques to safely cast variables to a different type. You can use pattern matching as well as the is and as operators to safely convert types.
-ms.date: 05/14/2021
+ms.date: 02/25/2022
 helpviewer_keywords: 
   - "cast operators [C#], as and is operators"
   - "as operator [C#]"

docs/csharp/fundamentals/tutorials/snippets/command-line-arguments/Program.cs

@@ -1,18 +1,11 @@
-using System;
+// The Length property provides the number of array elements.
+Console.WriteLine($"parameter count = {args.Length}");
 
-class CommandLine
+for (int i = 0; i < args.Length; i++)
 {
-    static void Main(string[] args)
-    {
-        // The Length property provides the number of array elements.
-        Console.WriteLine($"parameter count = {args.Length}");
-
-        for (int i = 0; i < args.Length; i++)
-        {
-            Console.WriteLine($"Arg[{i}] = [{args[i]}]");
-        }
-    }
+    Console.WriteLine($"Arg[{i}] = [{args[i]}]");
 }
+
 /* Output (assumes 3 cmd line args):
     parameter count = 3
     Arg[0] = [a]

docs/csharp/fundamentals/tutorials/snippets/command-line-arguments/command-line-arguments.csproj

@@ -2,8 +2,10 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net5.0</TargetFramework>
+    <TargetFramework>net6.0</TargetFramework>
     <RootNamespace>command_line_arguments</RootNamespace>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
   </PropertyGroup>
 
 </Project>

docs/csharp/fundamentals/tutorials/snippets/inheritance/Program.cs

@@ -1,17 +1,14 @@
-using System;
+namespace Inheritance;
 
-namespace inheritance
+class Program
 {
-    class Program
+    static void Main(string[] args)
     {
-        static void Main(string[] args)
-        {
-            Basic.Example.Main();
-            IsA_Namespace.Example.Main();
-            AccessExample.Main(args);
-            Example.Example.Main();
-            ClassNameExample.Main();
-            ClassExample.Main();
-        }
+        Basic.Example.Main();
+        IsA_Namespace.Example.Main();
+        AccessExample.Main(args);
+        Example.Example.Main();
+        ClassNameExample.Main();
+        ClassExample.Main();
     }
 }