Mark Rendle's .NET development blog.

My 20 Years with .NET

For the 20th birthday of .NET, a look back at my time with it.

21-Minute Read

It’s .NET’s 20th birthday: 20 years since Microsoft released v1.0 of their managed runtime, a Base Class Library, a couple of application frameworks, and the C# programming language. So I thought I’d do a retrospective of my 20 years working with .NET, because I’m extraordinarily vain and I assume people want to read stuff like this.

1.0 beta

It was some time in late 2001 when Microsoft released the beta version of their new framework. I’d just returned to programming after a brief stint as a professional stand-up comic, which I tried for a couple of years before deciding it wasn’t for me.

I was working for a company who shall remain nameless, developing and maintaining a CRM system for non-profits that was written in Gupta Team Developer. It was a dying platform, and we needed something to replace it. We were using Visual C++ and VB 6.0 to create ActiveX components, and Classic ASP for our web application interface, so Microsoft’s new hotness was an obvious line of investigation.

For the first beta, there was no Visual Studio, which made life interesting. No IntelliSense, and no real documentation either. The first program I wrote was a console app that reflected over every public type in the .NET Framework assemblies and generated a very basic set of HTML pages, one per type, divided into a directory per namespace. It didn’t extract the XML doc comments, it just dumped out all the methods, properties, constructors, etc for every type. I wrote the app in Vim, and compiled it from the command line with csc. And then I went browsing around my HTML pages, seeing what was there, comparing it with VB 6.0 and MFC.


By the time .NET 1.0 and Visual Studio .Net were released in February 2002, I’d written a handful of Windows Forms experiments and was convinced that this was the way forward. It was more fully formed out of the box than Java, fairly easy to learn if you were already familiar with the Microsoft ecosystem, and had some impressive features. ADO.NET! Data-binding! A WYSIWYG window designer! And C#! A language that felt like C++ but without having to remember to delete objects when you were finished with them! I started using it to write utilities for internal use, and lobbying to rewrite our product in C#. But that first version was very rough around the edges. The only resizable collection type was ArrayList, and the only dictionary was HashTable, neither of which were strongly typed. If you wanted a resizable list of int, you had to box them to add them to an ArrayList, and cast them back to int when you accessed them. And if you wanted to pass them to a method, that method had to know the ArrayList had ints in it. It was practically a dynamically typed environment. Microsoft had already announced that .NET and C# 2.0 would be getting “generics”, a magical new language feature that would fix this problem, so we decided to wait before starting the big porting project.


Four years passed between the releases of .NET 1.0 and 2.0, which is mad to think about now that we get a new version every year. It came with Visual Studio 2005, and the new generics feature was ground-breaking at the time. It was similar to C++ templates, but much easier to work with. It was also implemented properly, thanks to the Microsoft Research team who were working on a functional programming language for .NET. Generics in .NET were reified, which meant they were supported by the runtime and not just the compiler. Using reflection, you could create new generic objects and methods at runtime.

I finally got permission to start a project to rewrite our core product in C#. It was, in the best tradition of 1990s line-of-business applications, mostly just a collection of windows with too many textboxes and comboboxes, providing basic CRUD functionality but with an advanced “query-by-example” feature inspired by Informix 4GL. So rather than doing a screen-by-screen rewrite, I was building my own mini-framework to provide the same functionality.

At the time, .NET had a feature that was supposed to make working with complex database schema less of a chore: Strongly Typed DataSets. At the time, writing plain old C# objects was a chore. C# 2.0 did not have automatic properties like this:

public class Member
    public int Id { get; set; }

You had to provide your own backing field and implement the get and set manually, like this:

public class Member
    private int _id;

    public int Id
            return _id;
            _id = value;

Multiply that by a database with some 200 tables averaging 30 columns each. And then implementing the code to map from a SqlDataReader to those objects. NHibernate was in early development, but it was scary “Open Source” and we weren’t allowed to use it. So Strongly Typed DataSets, which you could pretty much just generate from your database and start using, were The Way.

Except they were terrible, and performance was horrible, and they were awful to work with, and data-binding to them from Windows Forms was hideous. But I persisted, and made progress, and had the core part of our core product running on .NET some time in 2006.

And then Microsoft released .NET 3.0.


Just two years after .NET 2.0, in November 2006, Microsoft released 3.0, at the same time as Windows Vista. The ambition for these two releases had been huge; a new file-system that was part database was one of the many features that never made it to the final code. But we did get Windows Presentation Foundation, a brand new desktop application framework that improved on Windows Forms in many, many ways. The data-binding was far better, for a start, and the layout was declared in XAML instead of hundreds of lines of C# generated by the WinForms designer. And applications developed with WPF looked modern.

So of course I decided to rewrite my rewrite in WPF.

At this point I had a junior developer working with me on the rewrite project, but there were three senior developers and three juniors still hard at work on the old Gupta Team Developer codebase, adding features that customers asked for and polishing the UI as best they could. And this junior developer and I were trying to catch up to them and get to a point where we had a new product with the same functionality as the old one. So throwing out thousands of lines of code and starting again with a brand new framework, which we had to learn as we went along, was probably one of the worse decisions I’ve made in my career.


Less than a year after 3.0, along came 3.5, bringing with it Language Integrated Query, or LINQ. This included LINQ-to-SQL, which allowed you to generate proper C# classes from your database and query against it right in your code. This was much better than Strongly Typed DataSets, so out they went and in came LINQ. More thousands of lines of code ditched and replaced with the new hotness.

By the end of 2008 my attempts to keep up with Microsoft’s new .NET features were seriously damaging my ability to deliver the promised rewrite. .NET just kept getting more and more awesome, and I couldn’t help chasing after every new feature they added. Except WCF. I never liked WCF.

I ended up burning myself out, and the company scrapped my project in favour of a VB.NET application from a company they’d acquired in the meantime. I didn’t want to do VB, so I quit and got a job at .NET Solutions, which sounded like my kind of place.

.NET Solutions

My new employers were a Microsoft Gold Partner and we got to work on some amazing projects. Getting excited about new features was pretty much part of the job, and projects were shorter so if something new landed while you were working on something, you could just finish that and then jump into a new one using the latest version. When I joined, they were just finishing up a .NET Micro Framework project that ran on a tiny circuit board connected to a fridge.

You know how during the World Cup Final there’s a spike in demand for electricity at half time? People think it’s all the kettles being boiled, but it’s not. It’s all the fridges being opened and warming up while people put milk in their teas and coffees, and then kicking in the refridgeration unit to cool down again. It spikes so much we have to buy extra electricity from France to cope with it.

The idea behind this project was that all the fridges would be able to talk to a web API that would say whether or not they could turn on. So when everybody put the milk back and closed the door, the fridges could coordinate and avoid all demanding extra electricity at once.

It was a fun project. The .NET Micro Framework didn’t have an HttpClient built in, so we had to implement our own over the Socket types. And there were inexplicable bugs which turned out to be due to voltage fluctuations causing problems with the custom ASIC on the board or some such thing.

.NET Solutions also had a bonus scheme that rewarded, among other things, blogging and speaking at user groups, so that was when I started doing that stuff. The first talk I did was about the LINQ-related features in .NET 3.5, particularly lambdas and extension methods, which allowed you to do some funky things with C#. For example, catching more than one exception type…

public static void Try<TException1, TException2>(
    Action action,
    Action<Exception> catchAction)
    catch (TException1 ex)
    catch (TException2 ex)

The third time I gave that talk was at the Developer Developer Developer conference at the Microsoft Campus in Reading. I was setting up when one of the other speakers came up to me and said “you know Jon Skeet’s in the audience?” So that was terrifying. But he loved it, and couldn’t help joining in and making suggestions for ways to push things even further, and I ended up pairing with him once the talk was finished, when I also discovered he’d been tweeting about it all the way through. That was the day I passed 1,000 followers on Twitter, thanks to .NET, C# and Jon.


In 2007, Scott Guthrie announced ASP.NET MVC, a .NET implementation of the Model/View/Controller pattern for building web applications. Up to then, the way to create web apps with .NET had been WebForms, an ambitious framework which tried to let developers pretend they were building a desktop application without having to worry about things like the HTTP protocol or round-trips to the browser. Unfortunately this required some ugly hacks, most notably ViewState, a potentially enormous chunk of data that was sent back and forth between browser and server on every request.

MVC did away with all of this, replacing it with Controllers that could handle HTTP requests and render Views, embracing the HTTP paradigm. It also came with Razor, a new way of combining C# with HTML to render pages from models.

But maybe the most interesting thing about ASP.NET MVC was that it was open source, with all the source code available on Microsoft’s CodePlex site. Before this, Microsoft, under Steve Ballmer, had been the sworn enemy of open source software; ASP.NET MVC was the first sign that this was starting to change.


.NET 4.0 and C# 4.0 were a weird release. The headline feature was the Dynamic Language Runtime, or DLR, and the dynamic keyword in C#. I think the main reason for it was to improve Office interop, but there were more interesting things you could do with it.

Around the same time that 4.0 came out, I’d been learning Ruby, and using an ORM called DataMapper which used Ruby’s method_missing feature to map dynamic properties and methods to database calls. There was a new base class in .NET 4.0, DynamicObject, that let you do pretty much the same thing, so as an experiment I wrote a simple library that let you have a dynamic object and call properties and methods on it to do database things, like this:

dynamic db = new Database(connectionString);
var order = db.Orders.FindById(id);

I called it Simple.Data, wrote some blogs about it and announced it on Twitter, and to my surprise it became quite popular. It’s had 800K downloads from NuGet, which isn’t bad. But as people asked for more and more features, and I added them, it became quite complicated and difficult to maintain. Eventually what it really needed was a ground-up rewrite, but by then I had a five year old daughter and a baby son and time was a scarce resource, so I wound the project down. Sorry if you liked it.


The big thing in .NET 4.5 was the Task-based asynchronous programming model. Instead of methods with Begin and End prefixes, we had methods that returned a Task which could trigger a callback when the underlying operation, usually some form of IO, completed. It was easier to use than the Begin/End model, but still resulted in code like this:

    .ContinueWith(r => r.ReadBodyAsStringAsync()
        .ContinueWith(body => ...))

The levels of callback nesting in a chain with a lot of Task-returning methods quickly got completely out of control.

C# 5.0

This was hugely improved with the release of C# 5.0, with the new async/await keywords, which made this kind of asynchronous programming much easier. Now we could just write code like this:

var response = await client.GetAsync(uri);
var body = await response.ReadBodyAsStringAsync();

This was much easier to understand and reason about, although there was an enormous amount of bike-shedding about what the actual keywords should be, particularly await, which many people thought sounded too much like Wait and implied that the current thread would be blocked waiting for the result, when what actually happened was that the current thread was returned to the thread pool and another one would be used when the Task completed.

I remember spending a fair amount of time going through code using either Task.ContinueWith or the old Begin/End methods and replacing it with async/await around this time, and also wishing there were an IAsyncEnumerable type.

4.6, 4.7, 4.8

After 4.5, .NET seemed to stagnate for a while. New features were added, but nothing that merited a major version bump. But the C# team were working on something completely new.

C# 6.0

Up to this point, the C# and VB.Net compilers had been written in C++. With C# 6.0, the compiler teams embarked on a multi-year project, codenamed Roslyn, to rewrite the compilers in their own languages. So the C# compiler was rewritten in C#, and the VB.Net compiler was rewritten in VB.Net. This would make it easier to add new features, although the only changes in C# 6.0 itself were some syntactic sugar for string interpolation and the like.

The really revolutionary thing about Roslyn, though, was that it represented a move to a Compiler-as-a-Service. The Roslyn packages were published on NuGet, and you could use them to parse, modify, analyse and generated C# code at runtime. It became possible to write your own code analysers and fixes and publish them as Visual Studio extensions or NuGet packages. More on this later…

Project K

In late 2015, on the ASP.Net Insiders mailing list, which I was lucky enough to be on, Damian Edwards and David Fowler announced a new project they’d been working on: a cut-down, light-weight and, most importantly, cross-platform version of .NET. It would run on Linux and Mac as well as Windows, and was optimised for writing web applications, without all the baggage of the full-fat, Windows-only .NET Framework. No Windows Forms, no WebForms, no WPF or WCF, just the minimum necessary to run ASP.NET MVC applications.

Moreover, Project K would be properly open source, developed in the open on GitHub, and accepting contributions from the community.

Obviously I downloaded and started playing with this right away, and I loved it. OK, so a huge chunk of the Base Class Library was missing, but it was C# and ASP.NET MVC and Web API working on Linux.

At the time I was a working at a place where the new Linux container technology, Docker, was being enthusiastically embraced. Apps were written in Node.js and Python to run in a cluster using an orchestration platform that I don’t remember the name of, but it wasn’t Kubernetes.

Project K meant that we could use .NET in this environment, and I found an actual use for it. I was working on a “web bug” tracking system that would follow users through the site and then off to external links to verify that they purchased something so we could send them a stuffed animal. This required generating a lot of UUIDs, and under heavy load. And it turns out that generating UUIDs is a compute intensive task, something that Node.js is not particularly good at.

So I wrote the simplest possible microservice in Project K, although it might have been called ASP.NET 5 by that point, which had a single endpoint that just returned a Guid as plain text. The Node.js app could call this service asynchronously, which is something that Node is very good at, and suddenly the system scaled. I don’t know if this was the first production use of the new .NET outside of Microsoft, but it must have been pretty close.

.NET Core 1.0

Project K became ASP.NET 5 became .NET Core 1.0. Along the way the promised new project.json project files were scrapped, which upset a lot of people, but the csproj files for Core applications were far simpler than those for .NET and despite being XML are mostly pretty simple to work with and edit manually when the need arises.

I remember watching a talk given by Damian and David at NDC Oslo where they talked about performance in .NET Core. Damian shared an anecdote wherein Kelly Sommers benchmarked the new Kestrel web server that was the engine of ASP.NET Core against her own Haywire engine, written in C. Kestrel was not fast: something like 70,000 requests per second compared to Haywire’s 1 million requests per second. Per Damian, he asked the Kestrel team why it was so slow, to which they responded “you didn’t tell us you wanted it to be fast.”

I don’t know how much of that is apocryphal, but there was a concerted effort to optimise the hell out of Kestrel, with a lot of contributions from Ben Adams, who had a vested interest in the project as his company, Ilyiad Games, make a game that runs on .NET on the server. By the time 1.0 was released, .NET Core was actually becoming competitive on the famous TechEmpower benchmarks.

Annoyingly, when .NET Core 1.0 launched, I was working at a place where new stuff was frowned upon so I had to continue working with .NET 4.something and WebAPI.

.NET Core 2.1

There was a 2.0 release, which was mainly concerned with adding back a lot of missing APIs from the .NET Framework, but the big release was .NET Core 2.1, which was when performance really became a feature of the new framework. 2.1 introduced the new Span<T> and Memory<T> types, which provided a better way of working with arrays or other chunks of memory, including unmanaged memory. This came with C# 7.2, which added a ref struct modifier that reduced copies when passing struct types between methods and is, I’m pretty sure, only really used for Span<T>; I’ve certainly never used it in my own code.

At this time I was working for one of the big investment banks, with a remit to extract functionality from a behemoth of a WPF application into shared services, and we were allowed to use .NET Core 2.1, so I got to play with it. But the biggest thing I actually achieved there was to use some of the .NET Core packages that were backward-compatible with .NET 4.x to add telemetry to the WPF application.

My favourite thing was a custom-written client for InfluxDB. The official client for .NET was quite inefficient: it allocated a lot of Dictionary<string,string> or Dictionary<string,object> objects for every line of metrics, and was too slow for our purposes. So I got to write an alternative client which used large byte arrays and wrote metrics passed through the new System.Diagnostics.DiagnosticSource model directly to Span<byte>s. My only regret was that we weren’t allowed to open source that library. If I can find the time, I might recreate it as an InfluxDB target for the new OpenTelemetry framework.

.NET Core 3.1

Again, there was a 3.0 release, but at this time Microsoft were using the .1 versions of .NET Core as the “LTS” (Long Term Servicing) releases. The big thing with 3.1 was that Windows Forms and WPF were ported over to Core, so you could build desktop Windows apps with it. Sadly this did not extend to making them cross-platform, which would be a huge effort since both WinForms and WPF are fairly thin wrappers over the underlying Windows APIs.

At the time .NET Core 3.1 was released, Scott Hunter announced that the next version would be .NET 5.0. .NET Core was becoming .NET; this would be where Microsoft invested time and energy in moving the platform forwards, and .NET 4.x would go into long term support, getting security updates and continuing to work on new versions of Windows, but no longer being improved or enhanced.

With this announcement came the news that the work of migrating .NET APIs to .NET Core was finished; if something hadn’t been migrated across now, it wasn’t going to be. This included Windows Communication Foundation, the framework that had been added way back in .NET 3.0 for building Service-Oriented Applications, usually using SOAP over HTTP as the protocol. The official Microsoft recommendation was to migrate WCF services to gRPC, the current standard for building distributed systems and microservices using the RPC pattern. gRPC had been added to ASP.NET Core as a first-class citizen, with a brand new implementation that was fast and efficient and worked with the rest of the ASP.NET Core stack.

As someone who had failed a Microsoft certification twice on the WCF test, and had fought against it on a variety of projects, I was delighted at this news, but it made a lot of people very angry. And I can understand why. I started playing with the new gRPC framework and was impressed, and realised that it mapped pretty easily to WCF’s RPC concepts. In fact, it mapped closely enough that I thought it might be possible to use Roslyn to convert WCF code to use gRPC instead.

I spent a week learning the Roslyn SDK and managed to get it doing a very basic conversion of a simple WCF service to gPRC, and could see that it was possible to do more complicated things as well, and Visual ReCode was born. Although I briefly considered making it open source, my wife would have killed me so I partnered with Gibraltar Software to sell it as a commercial product. I’m still working on it today.


This is not exactly a .NET version, but Unity is a game engine that uses C# as its scripting language, and provides most of the framework classes for building games. I put it here because it was around this time that I learned it. I used it to build an homage to the Club Penguin games with my son; he would draw the “graphics” in felt tip pen, and we’d scan it in and import it into the game, with me writing C# code and teaching him as we went along. I’ve also made a silly little game called Cheese Times Tables and actually released it on the various mobile App Stores. And I could do all of this with the fundamental knowledge of C# and .NET that I’ve picked up over the years writing line-of-business apps and web sites. I think that’s awesome. If I could find the time I’d be working on Extreme Croquet

5.0 and 6.0

And that brings us to today. I’ve been a .NET developer for 20 years, I’ve built things with WinForms, WebForms, WPF, WCF, MVC, the Micro Framework, Silverlight, Project K, .NET Core and .NET 6.0. For most of that time Microsoft have innovated on the framework and the C# language and compiler platform, and that innovation has accelerated since the Core era began. We now have Blazor, an amazing new web app framework that can run over a WebSocket between a browser and server, or be compiled to WebAssembly to run .NET code right in modern browsers. It’s easier to work with than WebForms ever was, while providing a lot of the same benefits such as simplified event handling and session state. And we’ve very nearly got MAUI, the new desktop and mobile application framework that is the evolution of Xamarin and a replacement for WPF, WinForms and UWP that also runs on Macs and might, one day, support Linux. There’s even a hybrid MAUI+Blazor model that wraps a Blazor Server application in a MAUI app, letting you target desktop, mobile and web with a single codebase.

With every release, .NET gets better performance across ASP.NET Core, Entity Framework Core, and all parts of the framework. C#, now on version 10 (with version 11 being loudly discussed on GitHub and Twitter), continues to evolve, offering ways of writing more expressive code with more optimal and safer runtime behaviour. The first previews of .NET 7.0 and C# 11 are likely to land any day now, and I’m looking forward to seeing what’s new there.

I don’t know if I’ll still be coding professionally in another 20 years; I’m getting on a bit and ideally I’ll be retired by then. But if there’s a celebration of 40 years of .NET in 2042, I hope to be there for the party.

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Nithish's Gravatar
Can you suggest me some course regarding to learn core mvc
Branislav Petrovic's Gravatar

Branislav Petrovic

Nice article! It’s a great retrospective over the 20 years of .NET.

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