C# *

No doubts that async/await pattern has significantly simplified working with asynchronous operations in C#. However, this simplification relates only to the situation when asynchronous operations are executed consequently. If we need to execute several asynchronous operations simultaneously (e.g. we need to call several micro-services) then we do not have many built-in capabilities and most probably Task.WhenAll will be used:

Task<SomeType1> someAsyncOp1 = SomeAsyncOperation1();
Task<SomeType2> someAsyncOp2 = SomeAsyncOperation2();
Task<SomeType3> someAsyncOp3 = SomeAsyncOperation3();
Task<SomeType4> someAsyncOp4 = SomeAsyncOperation4();
await Task.WhenAll(someAsyncOp1, someAsyncOp2, someAsyncOp4);
var result = new SomeContainer(
     someAsyncOp1.Result,someAsyncOp2.Result,someAsyncOp3.Result, someAsyncOp4.Result);

This is a working solution, but it is quite verbose and not very reliable (you can forget to add a new task to “WhenAll”). I would prefer something like that instead:

var result =  await 
    from r1 in SomeAsyncOperation1()
    from r2 in SomeAsyncOperation2()
    from r3 in SomeAsyncOperation3()
    from r4 in SomeAsyncOperation4()
    select new SomeContainer(r1, r2, r3, r4);

Further I will tell you what is necessary for this construction to work...

I'm putting part of older WebForms portions of my site that still run on bare metal to ASP.NET Core and Azure App Services, and while I'm doing that I realized that I want to make sure my staging sites don't get indexed by Google/Bing.

I already have a robots.txt, but I want one that's specific to production and others that are specific to development or staging. I thought about a number of ways to solve this. I could have a static robots.txt and another robots-staging.txt and conditionally copy one over the other during my Azure DevOps CI/CD pipeline.

Then I realized the simplest possible thing would be to just make robots.txt be dynamic. I thought about writing custom middleware but that sounded like a hassle and more code that needed. I wanted to see just how simple this could be.

Avalonia ui is a delightful framework to which you want to return again and again. So let's go back to it again and look at some of the features with my message box.

Today, we are announcing .NET Core 3.0 Preview 6. It includes updates for compiling assemblies for improved startup, optimizing applications for size with linker and EventPipe improvements. We’ve also released new Docker images for Alpine on ARM64.

• Download .NET Core 3.0 Preview 6 right now on Windows, macOS and Linux.

• Release notes have been published at dotnet/core. An API diff between Preview 5 and 6 is also available.

• ASP.NET Core and EF Core are also releasing updates today.

• If you missed it, check out the improvements we released in .NET Core 3.0 Preview 5, from last month.

I have originally posted this article in CodingSight blog
The second part of the article is available here

The need to do things in an asynchronous way – that is, dividing big tasks between multiple working units – was present long before the appearance of computers. However, when they did appear, this need became even more obvious. It is now 2019, and I’m writing this article on a laptop powered by an 8-core Intel Core CPU which, in addition to this, is simultaneously working on hundreds of processes, with the number of threads being even larger. Next to me, there lies a slightly outdated smartphone which I bought a couple of years ago – and it also houses an 8-core processor. Specialized web resources contain a wide variety of articles praising this year’s flagship smartphones equipped with 16-core CPUs. For less then $20 per hour, MS Azure can give you access to a 128-core virtual machine with 2 TB RAM. But, unfortunately, you cannot get the most out of this power unless you know how to control interaction between threads.

It's not a secret that Microsoft has been working on the 8-th version of C# language for quite a while. The new language version (C# 8.0) is already available in the recent release of Visual Studio 2019, but it's still in beta. This new version is going to have a few features implemented in a somewhat non-obvious, or rather unexpected, way. Nullable Reference types are one of them. This feature is announced as a means to fight Null Reference Exceptions (NRE).

I guess one of the most important issues in this topic is building an exception handling architecture in your application. This is interesting for many reasons. And the main reason, I think, is an apparent simplicity, which you don’t always know what to do with. All the basic constructs such as IEnumerable, IDisposable, IObservable, etc. have this property and use it everywhere. On the one hand, their simplicity tempts to use these constructs in different situations. On the other hand, they are full of traps which you might not get out. It is possible that looking at the amount of information we will cover you’ve got a question: what is so special about exceptional situations?

However, to make conclusions about building the architecture of exception classes we should learn some details about their classification. Because before building a system of types that would be clear for the user of code, a programmer should determine when to choose the type of error and when to catch or skip exceptions. So, let’s classify the exceptional situations (not the types of exceptions) based on various features.

Specifics of QueryProvider

QueryProvider can’t deal with this:

var result = _context.Humans
                      .Select(x => $"Name: {x.Name}  Age: {x.Age}")
                      .Where(x => x != "")
                      .ToList();

It can’t deal with any sentence using an interpolated string, but it’ll easily deal with this:

var result = _context.Humans
                      .Select(x => "Name " +  x.Name + " Age " + x.Age)
                      .Where(x => x != "")
                      .ToList();

The most painful thing is to fix bugs after turning on ClientEvaluation (exception for client-side calculation), since all Automapper profiles should be strictly analyzed for interpolation. Let’s find out what’s what and propose our solution to the problem.

Support of Visual Studio 2019 in PVS-Studio affected a number of components: the plugin itself, the command-line analyzer, the cores of the C++ and C# analyzers, and a few utilities. In this article, I will briefly explain what problems we encountered when implementing support of the IDE and how we addressed them.

Introduction

It’s time to talk about exceptions or, rather, exceptional situations. Before we start, let’s look at the definition. What is an exceptional situation?

This is a situation that makes the execution of current or subsequent code incorrect. I mean different from how it was designed or intended. Such a situation compromises the integrity of an application or its part, e.g. an object. It brings the application into an extraordinary or exceptional state.

But why do we need to define this terminology? Because it will keep us in some boundaries. If we don’t follow the terminology, we can get too far from a designed concept which may result in many ambiguous situations. Let’s see some practical examples:

 struct Number
 {
     public static Number Parse(string source)
     {
         // ...
         if(!parsed)
         {
             throw new ParsingException();
         }
         // ...
     }

     public static bool TryParse(string source, out Number result)
     {
        // ..
        return parsed;
     }
 }

This example seems a little strange, and it is for a reason. I made this code slightly artificial to show the importance of problems appearing in it. First, let’s look at the Parse method. Why should it throw an exception?

I notice that people often use construction like this:

var length = array.Length;
for (int i = 0; i < length; i++) {
    //do smth
}

They think that having a call to the Array.Length on each iteration will make CLR to take more time to execute the code. To avoid it they store the length value in a local variable.
Let’s find out (once and for all !) if this is a viable thing or using a temporary variable is a waste of time.

MessageBox — useful window for different GUI frameworks, but you can't find it in AvaloniaUI.
Let's try to do it.

February 2019 marked the release of ReactiveUI 9 — the cross-platform framework for building GUI applications on the Microsoft .NET platform. ReactiveUI is a tool for tight integration of reactive extensions with the MVVM design pattern. You could familiarize yourself with the framework via a series of videos or the welcome page of the documentation. The ReactiveUI 9 update includes numerous fixes and improvements, but probably the most crucial and interesting one is integration with the DynamicData framework, allowing you to work with dynamic collections in Reactive fashion. Let’s find out what we can use DynamicData for and how this powerful reactive framework works under the hood!

With this newest Blazor release we’re pleased to announce that Blazor is now in official preview! Blazor is no longer experimental and we are committing to ship it as a supported web UI framework including support for running client-side in the browser on WebAssembly.

A little over a year ago we started the Blazor experimental project with the goal of building a client web UI framework based on .NET and WebAssembly. At the time Blazor was little more than a prototype and there were lots of open questions about the viability of running .NET in the browser. Since then we’ve shipped nine experimental Blazor releases addressing a variety of concerns including component model, data binding, event handling, routing, layouts, app size, hosting models, debugging, and tooling. We’re now at the point where we think Blazor is ready to take its next step.

Some days ago we announced improved Razor tooling support in Visual Studio Code with the latest C# extension. This latest release includes improved Razor diagnostics and support for tag helpers and Blazor apps.

This article will show you the basics of types internals, as of course an example in which the memory for the reference type will be allocated completely on the stack (this is because I am a full-stack programmer).

Disclaimer

This article does not contain material that should be used in real projects. It is simply an extension of the boundaries in which a programming language is perceived.

Before proceeding with the story, I strongly recommend you to read the first post about StructLayout, because there is an example that will be used in this article (However, as always).

I propose to look at the internals that are behind the simple lines of initializing of the objects, calling methods, and passing parameters. And, of course, we will use this information in practice — we will subtract the stack of the calling method.

Disclaimer

Before proceeding with the story, I strongly recommend you to read the first post about StructLayout, there is an example that will be used in this article.

All code behind the high-level one is presented for the debug mode, because it shows the conceptual basis. JIT optimization is a separate big topic that will not be covered here.

I would also like to warn that this article does not contain material that should be used in real projects.

First — theory

Any code eventually becomes a set of machine commands. Most understandable is their representation in the form of Assembly language instructions that directly correspond to one (or several) machine instructions.

Multithreading

Now let’s talk about thin ice. In the previous sections about IDisposable we touched one very important concept that underlies not only the design principles of Disposable types but any type in general. This is the object’s integrity concept. It means that at any given moment of time an object is in a strictly determined state and any action with this object turns its state into one of the variants that were pre-determined while designing a type of this object. In other words, no action with the object should turn it into an undefined state. This results in a problem with the types designed in the above examples. They are not thread-safe. There is a chance the public methods of these types will be called when the destruction of an object is in progress. Let’s solve this problem and decide whether we should solve it at all.

This chapter was translated from Russian jointly by author and by professional translators. You can help us with translation from Russian or English into any other language, primarily into Chinese or German.

Also, if you want thank us, the best way you can do that is to give us a star on github or to fork repository github/sidristij/dotnetbook.

Hello. This time we continue to laugh at the normal method call. I propose to get acquainted with the method call with parameters without passing parameters. We will also try to convert the reference type to a number — its address, without using pointers and unsafe code.

Memory<T> and ReadOnlyMemory<T>

There are two visual differences between Memory<T> and Span<T>. The first one is that Memory<T> type doesn’t contain ref modifier in the header of the type. In other words, the Memory<T> type can be allocated both on the stack while being either a local variable, or a method parameter, or its returned value and on the heap, referencing some data in memory from there. However, this small difference creates a huge distinction in the behavior and capabilities of Memory<T> compared to Span<T>. Unlike Span<T> that is an instrument for some methods to use some data buffer, the Memory<T> type is designed to store information about the buffer, but not to handle it. Thus, there is the difference in API.

• Memory<T> doesn’t have methods to access the data that it is responsible for. Instead, it has the Span property and the Slice method that return an instance of the Span type.
• Additionally, Memory<T> contains the Pin() method used for scenarios when a stored buffer data should be passed to unsafe code. If this method is called when memory is allocated in .NET, the buffer will be pinned and will not move when GC is active. This method will return an instance of the MemoryHandle structure, which encapsulates GCHandle to indicate a segment of a lifetime and to pin array buffer in memory.

This chapter was translated from Russian jointly by author and by professional translators. You can help us with translation from Russian or English into any other language, primarily into Chinese or German.

Also, if you want thank us, the best way you can do that is to give us a star on github or to fork repository github/sidristij/dotnetbook.