My favorite new features in C# 9 (.NET 5)

This week .NET Conference 2020 took held between 10-12 November. During the conference, .NET 5 and C# 9.0 was officially released.
In this video, I am going to walk through three features of C# 9.0, which are my favorite ones.
And they are:
1. Init only setters
2. Record types
3. Top-level statements
In my opinion, Record type will be one of the most used features of C# 9.0. It is at least my favorite one. Creating an immutable type was never been so easy.
Init only setters are the enabler behind the record types. It is the feature that is used internally to achieve the feature of the record type.
Top-level statements also are going to be highly used, especially when working with serverless technologies like Azure functions or AWS Lambda.
Last year I did a video on my top 5 favorite features of C# 8.0, you can check it out on KZbin here: • Top Five C# 8 Features...
My blog site where I write exclusively about .NET Core (.NET 5 going forward) is here: dotnetcorecent...

[@paulohincdig]

Thank you for your explanation and the way you make it so easy.

[@DotNetCoreCentral]

@Paulo Duarte, thanks for watching!

[@davidharrington1133]

ToString() on a record also has a sensible string description by default.

[@saurabhchauhan232]

Very nice simple and clear examples

[@DotNetCoreCentral]

@Saurabh Chauhan, thanks for watching!

[@techrelated2417]

Very useful and easy to understand. Thanks for the video!!

[@DotNetCoreCentral]

@Tech Related, thanks for watching!

[@elliottevan9348]

I guess I am quite randomly asking but does anyone know of a good site to stream newly released movies online ?

[@VijayKumar-wy9ku]

Top notch content!

[@DotNetCoreCentral]

Thanks!

[@christophertanghare4884]

Thanks for the video 😁 great job

[@DotNetCoreCentral]

@Christopher Tanghare, thanks!

[@ashutoshsoni3017]

very quick and simple explanation. Thanks Brother.

[@DotNetCoreCentral]

@Ashutosh Soni, thanks for watching!

[@errrzarrr]

_init_ keyword: I think we already have OOP encapsulation and access modifiers ( _private_ keyword) for that. Also, what about _const_ and _readonly_ keywords then, what are they for?

[@DotNetCoreCentral]

@Roberto M., to my understanding, init, const, and read-only are three very different and distinct features. init - allowed to set only using objection initialization, where the property value is not set through a constructor. Hence it works similar to how a real-only and constructor based object initialization works with a property based initialization scenario. Hence at a very high level conceptually it is the same read-only, but in terms of implementation, it is very different. Both promote immutability at their core. const - on the other hand, is to define compiled time and is a class-level variable that is constant in nature. Also, you can consider const = static read-only.

[@aj.arunkumar]

Nice one... But when we remove the Program class and Main method, shouldn't be there an error 'args not defined' ... ? or is it like args the default name for cmd line args...?

[@DotNetCoreCentral]

@Arun Kumar A.J, The framework automatically creates string[] args and passes it to the top-level calls, and that is why the compiler does not complain about it.

[@davimezalira]

Very useful.. tks

[@DotNetCoreCentral]

@Davi Mezalira, thanks for watching!

[@gopalakrishnanm9349]

Nice.pls put a video for major changes in dotnet 5 Because I don't know why I'm using dotnet 5 instead of dotnet 3.1

[@DotNetCoreCentral]

@Gopi HB, thanks for watching. And I will surely do a video on .NET 5 changes.

[@gopalakrishnanm9349]

@@DotNetCoreCentral thanks

[@DotNetCoreCentral]

@@gopalakrishnanm9349 you are welcome!

[@mahi-lapse]

Simple and nice explanation, thanks

[@DotNetCoreCentral]

@Mahi Uddin, thanks for watching!

[@sujitwarrier4857]

"with" is like the spread operator in Javascript

[@DotNetCoreCentral]

@Sujit Warrier, to my understanding with and spread, are nothing alike. To my understanding spread in JavaScript is similar to Ranges in C#

[@anassnassim]

Thanks for the video what is the best path for creating a website with asp .net core what I should learn?

[@DotNetCoreCentral]

@Anass nasim, in my opinion, a JavaScript SPA framework like Angular or React is a better option for creating a website, whereas you can use .NET Web API for REST services providing data to the website. The Blazor web assembly is also an option, but I am currently exploring it and not yet convinced it's a better alternative to JavaScript.

[@hkpeaks]

C# is amazing, using c# to read 70MB CSV file with data row 1,000,000 => only 1.1 second, plus generate web summary report => 1.2 second

[@DotNetCoreCentral]

@Freeware Web BI Tool 【你快 youFast】thanks for watching!

[@AshishSingh146]

Thanks you 4 explanation.

[@DotNetCoreCentral]

@Ashish Singh, thanks for watching!

[@subrataranjanpal6518]

Wonderful !!!

[@DotNetCoreCentral]

@Subrata Ranjan Pal, thanks for watching!

[@rynox77]

Using the with example, is a new instance of the record constructed or, put another way, is memory allocated for an additional instance of the record with the "with" statement? It must be if records are immutable, right?

[@rynox77]

Also, what are the ramifications of using the special case pattern with record types?

[@DotNetCoreCentral]

@Ryan McAtee, a new instance of the record is created (with additional memory allocation). As you guessed since it's immutable by design.

[@DotNetCoreCentral]

@@rynox77 I do not think there is any. What kind of ramifications you are thinking that might be a side effect?

[@rynox77]

@@DotNetCoreCentral Given the following: record Person(string FirstName, string LastName); It looks like for my special case, record PersonNotFound : Person... it requires the constructor public PersonNotFound() : base(default, default) { }.

[@DotNetCoreCentral]

@@rynox77 I would be interested in knowing what is the special case, just out of curiosity. I have not come across this situation yet, but it's of course too early.

[@rajkgoel77]

Using 'with' statement can we join multiple instances of different classes? If yes, how would it work in case of overlapping property names? Also, would methods from these different instances be available in newly created instance?

[@DotNetCoreCentral]

@Khaleefa, no you cannot join, it is more like inheritance than join. So you can use "with" keyword only with one record type. The answer to your second question is yes.

[@ProperComment]

Just wow!!

[@DotNetCoreCentral]

@The Red Baron, thanks!

[@user-ir5vb7vv5e]

Thank you

[@DotNetCoreCentral]

@Александр Бабаев, thank you for watching the video!

[@Flaflo]

I am glad they are taking features from kotlin over to c# thats really nice.

[@chezchezchezchez]

Which features?

[@DotNetCoreCentral]

@Flaflo, Thanks for watching! As far as I know, features like record type existed in functional programming languages like Scala and F# way before kotlin was even created. But I might be wrong.

[@errrzarrr]

I think they are general concepts. That's what I think.

[@DotNetCoreCentral]

@@errrzarrr thanks for watching the video.

[@LuigiZambetti]

Why don't you make a playlist on Blazor or developing web applications with .NET 5.0?

[@DotNetCoreCentral]

@Luigi Zambetti, I will create on, thanks for the suggestion.

[@DotNetCoreCentral]

@Nothing IsReal I can try this out in future episodes when I start my series on AWS and Azure.

[@voswouter87]

Why is .net not cls compliant?

[@DotNetCoreCentral]

@Wouter Vos, thanks for watching the video. I am not sure I understand your question. CLS is for languages, and .NET Framework enforces the CLS compliance, so CLS is meaningless without .NET so to speak. And if you meant about C#, then C# is 100% CLS compliant, otherwise, it will not be able to run inside a .NET compiler. I hope this answers your question.

[@voswouter87]

@@DotNetCoreCentral The coding style at my company includes CLS compliance as a good practice for better code. However when using code from ASP.NET Core almost everything isn't, so we end up having to turn it off. Does ASP.NET Core also have many external imports? I'd expect not and thus it would be very easy to make it CLS compliant. What would be lost if it was?

[@DotNetCoreCentral]

@@voswouter87 Hi, I am sorry, but I am still not able to understand what all in ASP.NET Core is CLS Compliant, so it is hard for me to say how different it will be in .NET 5.