8. Code Contracts | C# Programming Cookbook

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Table Of Contents

C# Programming Cookbook

By : Dirk Strauss

C# Programming Cookbook

By: Dirk Strauss

Overview of this book

During your application development workflow, there is always a moment when you need to get out of a tight spot. Through a recipe-based approach, this book will help you overcome common programming problems and get your applications ready to face the modern world. We start with C# 6, giving you hands-on experience with the new language features. Next, we work through the tasks that you perform on a daily basis such as working with strings, generics, and lots more. Gradually, we move on to more advanced topics such as the concept of object-oriented programming, asynchronous programming, reactive extensions, and code contracts. You will learn responsive high performance programming in C# and how to create applications with Azure. Next, we will review the choices available when choosing a source control solution. At the end of the book, we will show you how to create secure and robust code, and will help you ramp up your skills when using the new version of C# 6 and Visual Studio

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Sections

Conventions

Reader feedback

Customer support

Free Chapter

1. New Features in C# 6.0

1. New Features in C# 6.0

Introduction

Creating your Visual Studio project

String interpolation

Null-conditional operator

Initializers for auto-implemented properties and getter-only auto properties

Index initializers

The nameof expressions

Expression-bodied functions and properties

Using static

Exception filters

Using await operator in catch and finally blocks

2. Classes and Generics

2. Classes and Generics

Introduction

Creating and implementing an abstract class

Creating and implementing an interface

Creating and using a generic class or method

Creating and using a generic interface

3. Object-Oriented Programming in C#

3. Object-Oriented Programming in C#

Introduction

Using inheritance in C#

Using abstraction

Leveraging encapsulation

Implementing polymorphism

Single responsibility principle

Open/closed principle

4. Composing Event-Based Programs Using Reactive Extensions

4. Composing Event-Based Programs Using Reactive Extensions

Introduction

Installing Rx

Events versus observables

Using LINQ to perform queries

Using schedulers in Rx

Debugging lambda expressions

5. Create Microservices on Azure Service Fabric

5. Create Microservices on Azure Service Fabric

Introduction

Downloading and installing Service Fabric

Creating a Service Fabric application with a stateless actor service

Using Service Fabric Explorer

6. Making Apps Responsive with Asynchronous Programming

6. Making Apps Responsive with Asynchronous Programming

Introduction

Return types of asynchronous functions

Handling tasks in asynchronous programming

Exception handling in asynchronous programming

7. High Performance Programming Using Parallel and Multithreading in C#

7. High Performance Programming Using Parallel and Multithreading in C#

Introduction

Creating and aborting a low-priority background thread

Increasing maximum thread pool size

Creating multiple threads

Locking one thread until the contended resources are available

Invoking parallel calls to methods using Parallel.Invoke

Using a parallel foreach loop to run multiple threads

Cancelling a parallel foreach loop

Catching errors in parallel foreach loops

Debugging multiple threads

8. Code Contracts

8. Code Contracts

Introduction

Downloading, installing, and integrating code contracts into Visual Studio

Creating code contract preconditions

Creating code contract postconditions

Creating code contract invariant

Creating code contract Assert and Assume methods

Creating code contract ForAll method

Creating code contract ValueAtReturn method

Creating code contract Result method

Using code contracts on abstract classes

Using contract abbreviator methods

Creating tests using IntelliTest

Using code contracts in extension methods

9. Regular Expressions

9. Regular Expressions

Introduction

Getting started with regex

Matching a valid date

Sanitizing input

Dynamic regex matching

10. Choosing and Using a Source Control Strategy

10. Choosing and Using a Source Control Strategy

Introduction

Setting up Visual Studio account management and determining which source control solution is best for you

Setting up Visual Studio GitHub integration, checking in code for the first time, and checking in changes

Working as a team using GitHub, and handling and resolving conflicts in code

11. Creating a Mobile Application in Visual Studio

11. Creating a Mobile Application in Visual Studio

Introduction

Installing Xamarin and other required components

Creating an Android Visual Studio project using Apache Cordova

Creating an iOS application using Xamarin Forms

12. Writing Secure Code and Debugging in Visual Studio

12. Writing Secure Code and Debugging in Visual Studio

Introduction

Encrypting and storing passwords correctly

Using SecureString in code

Securing sensitive parts of App.config/web.config

Preventing SQL injection attacks

Using Diagnostic Tools and Historical Debugging

Setting conditional breakpoints

Using PerfTips to identify bottlenecks in code

13. Creating a Web Application in Azure

13. Creating a Web Application in Azure

Introduction

Creating a database in Azure for testing

Creating a web application and hosting on Azure

Using virtual machines on Azure

Index

Index

Creating code contract ValueAtReturn method

The best example we can think of when using the code contract ValueAtReturn is out parameters. Personally, I do not use out parameters often, but there are times when you need to use them. Code contracts make provision for this, and you can check the value at the time it is returned.

Getting ready

We will create a simple method that subtracts a value from a parameter. The out parameter will be validated by the code contract, and the result will be output to the console window.

How to do it…

Before you go on, ensure that you have added the code contracts using statement to the top of your Recipes.cs class file:
```
using System.Diagnostics.Contracts;
```
In the Recipes class, create a new method called ValidOutValue() and pass an out parameter called secureValue to it:
```
public static void ValidOutValue(out int secureValue)
{
    
}
```
Finally, add Contract.ValueAtReturn to the method. Interestingly, you will note that this needs to be contained in Contract.Ensures...

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