The history of C#

This article provides a history of each major release of the C# language. The C# team is continuing to innovate and add new features. Detailed language feature status, including features considered for upcoming releases can be found on the dotnet/roslyn repository on GitHub.


The C# language relies on types and methods in what the C# specification defines as a standard library for some of the features. The .NET platform delivers those types and methods in a number of packages. One example is exception processing. Every throw statement or expression is checked to ensure the object being thrown is derived from Exception. Similarly, every catch is checked to ensure that the type being caught is derived from Exception. Each version may add new requirements. To use the latest language features in older environments, you may need to install specific libraries. These dependencies are documented in the page for each specific version. You can learn more about the relationships between language and library for background on this dependency.

The C# build tools consider the latest major language release the default language version. There may be point releases between major releases, detailed in other articles in this section. To use the latest features in a point release, you need to configure the compiler language version and select the version. There have been three-point releases since C# 7.0:

C# version 1.0

When you go back and look, C# version 1.0, released with Visual Studio .NET 2002, looked a lot like Java. As part of its stated design goals for ECMA, it sought to be a "simple, modern, general-purpose object-oriented language." At the time, looking like Java meant it achieved those early design goals.

But if you look back on C# 1.0 now, you'd find yourself a little dizzy. It lacked the built-in async capabilities and some of the slick functionality around generics you take for granted. As a matter of fact, it lacked generics altogether. And LINQ? Not available yet. Those additions would take some years to come out.

C# version 1.0 looked stripped of features, compared to today. You'd find yourself writing some verbose code. But yet, you have to start somewhere. C# version 1.0 was a viable alternative to Java on the Windows platform.

The major features of C# 1.0 included:

C# version 1.2

C# version 1.2 shipped with Visual Studio .NET 2003. It contained a few small enhancements to the language. Most notable is that starting with this version, the code generated in a foreach loop called Dispose on an IEnumerator when that IEnumerator implemented IDisposable.

C# version 2.0

Now things start to get interesting. Let's take a look at some major features of C# 2.0, released in 2005, along with Visual Studio 2005:

Other C# 2.0 features added capabilities to existing features:

  • Getter/setter separate accessibility
  • Method group conversions (delegates)
  • Static classes
  • Delegate inference

While C# may have started as a generic Object-Oriented (OO) language, C# version 2.0 changed that in a hurry. Once they had their feet under them, they went after some serious developer pain points. And they went after them in a significant way.

With generics, types and methods can operate on an arbitrary type while still retaining type safety. For instance, having a List<T> lets you have List<string> or List<int> and perform type-safe operations on those strings or integers while you iterate through them. Using generics is better than creating a ListInt type which derives from ArrayList or casting from Object for every operation.

C# version 2.0 brought iterators. To put it succinctly, iterators let you examine all the items in a List (or other Enumerable types) with a foreach loop. Having iterators as a first-class part of the language dramatically enhanced readability of the language and people's ability to reason about the code.

And yet, C# continued to play a bit of catch-up with Java. Java had already released versions that included generics and iterators. But that would soon change as the languages continued to evolve apart.

C# version 3.0

C# version 3.0 came in late 2007, along with Visual Studio 2008, though the full boat of language features would actually come with .NET Framework version 3.5. This version marked a major change in the growth of C#. It established C# as a truly formidable programming language. Let's take a look at some major features in this version:

In retrospect, many of these features seem both inevitable and inseparable. They all fit together strategically. It's generally thought that C# version's killer feature was the query expression, also known as Language-Integrated Query (LINQ).

A more nuanced view examines expression trees, lambda expressions, and anonymous types as the foundation upon which LINQ is constructed. But, in either case, C# 3.0 presented a revolutionary concept. C# 3.0 had begun to lay the groundwork for turning C# into a hybrid Object-Oriented / Functional language.

Specifically, you could now write SQL-style, declarative queries to perform operations on collections, among other things. Instead of writing a for loop to compute the average of a list of integers, you could now do that as simply as list.Average(). The combination of query expressions and extension methods made it look as though that list of integers had gotten a whole lot smarter.

It took time for people to really grasp and integrate the concept, but they gradually did. And now, years later, code is much more concise, simple, and functional.

C# version 4.0

C# version 4.0, released with Visual Studio 2010, would have had a difficult time living up to the groundbreaking status of version 3.0. With version 3.0, C# had moved the language firmly out from the shadow of Java and into prominence. The language was quickly becoming elegant.

The next version did introduce some interesting new features:

Embedded interop types alleviated a deployment pain. Generic covariance and contravariance give you more power to use generics, but they're a bit academic and probably most appreciated by framework and library authors. Named and optional parameters let you eliminate many method overloads and provide convenience. But none of those features are exactly paradigm altering.

The major feature was the introduction of the dynamic keyword. The dynamic keyword introduced into C# version 4.0 the ability to override the compiler on compile-time typing. By using the dynamic keyword, you can create constructs similar to dynamically typed languages like JavaScript. You can create a dynamic x = "a string" and then add six to it, leaving it up to the runtime to sort out what should happen next.

Dynamic binding gives you the potential for errors but also great power within the language.

C# version 5.0

C# version 5.0, released with Visual Studio 2012, was a focused version of the language. Nearly all of the effort for that version went into another groundbreaking language concept: the async and await model for asynchronous programming. Here is the major features list:

See Also

The caller info attribute lets you easily retrieve information about the context in which you're running without resorting to a ton of boilerplate reflection code. It has many uses in diagnostics and logging tasks.

But async and await are the real stars of this release. When these features came out in 2012, C# changed the game again by baking asynchrony into the language as a first-class participant. If you've ever dealt with long running operations and the implementation of webs of callbacks, you probably loved this language feature.

C# version 6.0

With versions 3.0 and 5.0, C# had added major new features in an object-oriented language. With version 6.0, released with Visual Studio 2015, it would go away from doing a dominant killer feature and instead release many smaller features that made C# programming more productive. Here are some of them:

Other new features include:

  • Index initializers
  • Await in catch/finally blocks
  • Default values for getter-only properties

Each of these features is interesting in its own right. But if you look at them altogether, you see an interesting pattern. In this version, C# eliminated language boilerplate to make code more terse and readable. So for fans of clean, simple code, this language version was a huge win.

They did one other thing along with this version, though it's not a traditional language feature in itself. They released Roslyn the compiler as a service. The C# compiler is now written in C#, and you can use the compiler as part of your programming efforts.

C# version 7.0

C# version 7.0 was released with Visual Studio 2017. This version has some evolutionary and cool stuff in the vein of C# 6.0, but without the compiler as a service. Here are some of the new features:

Other features included:

All of these features offer cool new capabilities for developers and the opportunity to write even cleaner code than ever. A highlight is condensing the declaration of variables to use with the out keyword and by allowing multiple return values via tuple.

But C# is being put to ever broader use. .NET Core now targets any operating system and has its eyes firmly on the cloud and on portability. These new capabilities certainly occupy the language designers' thoughts and time, in addition to coming up with new features.

C# version 7.1

C# started releasing point releases with C# 7.1. This version added the language version selection configuration element, three new language features, and new compiler behavior.

The new language features in this release are:

Finally, the compiler has two options -refout and -refonly that control reference assembly generation.

C# version 7.2

C# 7.2 added several small language features:

C# version 7.3

There are two main themes to the C# 7.3 release. One theme provides features that enable safe code to be as performant as unsafe code. The second theme provides incremental improvements to existing features. In addition, new compiler options were added in this release.

The following new features support the theme of better performance for safe code:

The following enhancements were made to existing features:

  • You can test == and != with tuple types.
  • You can use expression variables in more locations.
  • You may attach attributes to the backing field of auto-implemented properties.
  • Method resolution when arguments differ by in has been improved.
  • Overload resolution now has fewer ambiguous cases.

The new compiler options are:

  • -publicsign to enable Open Source Software (OSS) signing of assemblies.
  • -pathmap to provide a mapping for source directories.

C# version 8.0

C# 8.0 is the first major C# release that specifically targets .NET Core. Some features rely on new CLR capabilities, others on library types added only in .NET Core. C# 8.0 adds the following features and enhancements to the C# language:

Default interface members require enhancements in the CLR. Those features were added in the CLR for .NET Core 3.0. Ranges and indexes, and asynchronous streams require new types in the .NET Core 3.0 libraries. Nullable reference types, while implemented in the compiler, is much more useful when libraries are annotated to provide semantic information regarding the null state of arguments and return values. Those annotations are being added in the .NET Core libraries.

Article originally published on the NDepend blog, courtesy of Erik Dietrich and Patrick Smacchia.