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.

C# version 12

Released November 2023

The following features were added in C# 12:

And, Interceptors - was released as a Preview feature.

Overall, C# 12 provides new features that make you more productive writing C# code. Syntax you already knew is available in more places. Other syntax enables consistency for related concepts.

C# version 11

Released November 2022

The following features were added in C# 11:

C# 11 introduces generic math and several features that support that goal. You can write numeric algorithms once for all number types. There's more features to make working with struct types easier, like required members and auto-default structs. Working with strings gets easier with Raw string literals, newline in string interpolations, and UTF-8 string literals. Features like file local types enable source generators to be simpler. Finally, list patterns add more support for pattern matching.

C# version 10

Released November 2021

C# 10 adds the following features and enhancements to the C# language:

More features were available in preview mode. In order to use these features, you must set <LangVersion> to Preview in your project:

C# 10 continues work on themes of removing ceremony, separating data from algorithms, and improved performance for the .NET Runtime.

Many of the features mean you type less code to express the same concepts. Record structs synthesize many of the same methods that record classes do. Structs and anonymous types support with expressions. Global using directives and file scoped namespace declarations mean you express dependencies and namespace organization more clearly. Lambda improvements make it easier to declare lambda expressions where they're used. New property patterns and deconstruction improvements create more concise code.

The new interpolated string handlers and AsyncMethodBuilder behavior can improve performance. These language features were applied in the .NET Runtime to achieve performance improvements in .NET 6.

C# 10 also marks more of a shift to the yearly cadence for .NET releases. Because not every feature can be completed in a yearly timeframe, you can try a couple of "preview" features in C# 10. Both generic attributes and static abstract members in interfaces can be used, but these preview features might change before their final release.

C# version 9

Released November 2020

C# 9 was released with .NET 5. It's the default language version for any assembly that targets the .NET 5 release. It contains the following new and enhanced features:

C# 9 continues three of the themes from previous releases: removing ceremony, separating data from algorithms, and providing more patterns in more places.

Top level statements means your main program is simpler to read. There's less need for ceremony: a namespace, a Program class, and static void Main() are all unnecessary.

The introduction of records provides a concise syntax for reference types that follow value semantics for equality. You use these types to define data containers that typically define minimal behavior. Init-only setters provide the capability for nondestructive mutation (with expressions) in records. C# 9 also adds covariant return types so that derived records can override virtual methods and return a type derived from the base method's return type.

The pattern matching capabilities expanded in several ways. Numeric types now support range patterns. Patterns can be combined using and, or, and not patterns. Parentheses can be added to clarify more complex patterns:

C# 9 includes new pattern matching improvements:

  • Type patterns match an object matches a particular type
  • Parenthesized patterns enforce or emphasize the precedence of pattern combinations
  • Conjunctive and patterns require both patterns to match
  • Disjunctive or patterns require either pattern to match
  • Negated not patterns require that a pattern doesn't match
  • Relational patterns require the input be less than, greater than, less than or equal, or greater than or equal to a given constant

These patterns enrich the syntax for patterns. Consider these examples:

public static bool IsLetter(this char c) =>
    c is >= 'a' and <= 'z' or >= 'A' and <= 'Z';

With optional parentheses to make it clear that and has higher precedence than or:

public static bool IsLetterOrSeparator(this char c) =>
    c is (>= 'a' and <= 'z') or (>= 'A' and <= 'Z') or '.' or ',';

One of the most common uses is a new syntax for a null check:

if (e is not null)
    // ...

Any of these patterns can be used in any context where patterns are allowed: is pattern expressions, switch expressions, nested patterns, and the pattern of a switch statement's case label.

Another set of features supports high-performance computing in C#:

  • The nint and nuint types model the native-size integer types on the target CPU.
  • Function pointers provide delegate-like functionality while avoiding the allocations necessary to create a delegate object.
  • The localsinit instruction can be omitted to save instructions.

Performance and interop

Another set of improvements supports scenarios where code generators add functionality:

  • Module initializers are methods that the runtime calls when an assembly loads.
  • Partial methods support new accessibly modifiers and non-void return types. In those cases, an implementation must be provided.

Fit and finish features

C# 9 adds many other small features that improve developer productivity, both writing and reading code:

  • Target-type new expressions
  • static anonymous functions
  • Target-type conditional expressions
  • Extension GetEnumerator() support for foreach loops
  • Lambda expressions can declare discard parameters
  • Attributes can be applied to local functions

The C# 9 release continues the work to keep C# a modern, general-purpose programming language. Features continue to support modern workloads and application types.

C# version 8.0

Released September 2019

C# 8.0 is the first major C# release that specifically targets .NET Core. Some features rely on new Common Language Runtime (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.

C# version 7.3

Released May 2018

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. New compiler options were also added in this release.

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

  • You can access fixed fields without pinning.
  • You can reassign ref local variables.
  • You can use initializers on stackalloc arrays.
  • You can use fixed statements with any type that supports a pattern.
  • You can use more generic constraints.

The following enhancements were made to existing features:

  • You can test == and != with tuple types.
  • You can use expression variables in more locations.
  • You can attach attributes to the backing field of auto-implemented properties.
  • Method resolution when arguments differ by in was 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 7.2

Released November 2017

C# 7.2 added several small language features:

  • Initializers on stackalloc arrays.
  • Use fixed statements with any type that supports a pattern.
  • Access fixed fields without pinning.
  • Reassign ref local variables.
  • Declare readonly struct types, to indicate that a struct is immutable and should be passed as an in parameter to its member methods.
  • Add the in modifier on parameters, to specify that an argument is passed by reference but not modified by the called method.
  • Use the ref readonly modifier on method returns, to indicate that a method returns its value by reference but doesn't allow writes to that object.
  • Declare ref struct types, to indicate that a struct type accesses managed memory directly and must always be stack allocated.
  • Use additional generic constraints.
  • Non-trailing named arguments:
    • Positional arguments can follow named arguments.
  • Leading underscores in numeric literals:
    • Numeric literals can now have leading underscores before any printed digits.
  • private protected access modifier:
    • The private protected access modifier enables access for derived classes in the same assembly.
  • Conditional ref expressions:
    • The result of a conditional expression (?:) can now be a reference.

C# version 7.1

Released August 2017

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:

  • async Main method
    • The entry point for an application can have the async modifier.
  • default literal expressions
    • You can use default literal expressions in default value expressions when the target type can be inferred.
  • Inferred tuple element names
    • The names of tuple elements can be inferred from tuple initialization in many cases.
  • Pattern matching on generic type parameters
    • You can use pattern match expressions on variables whose type is a generic type parameter.

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

C# version 7.0

Released March 2017

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. Here are some of the new features:

Other features included:

All of these features offer new capabilities for developers and the opportunity to write 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. .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 6.0

Released July 2015

Version 6.0, released with Visual Studio 2015, released 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

If you look at these features together, you see an interesting pattern. In this version, C# started to eliminate 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 5.0

Released August 2012

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's the major features list:

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.

C# version 4.0

Released April 2010

C# version 4.0, released with Visual Studio 2010, introduced some interesting new features:

Embedded interop types eased the deployment pain of creating COM interop assemblies for your application. 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 3.0

Released November 2007

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. This 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 began 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 a list of integers a whole lot smarter.

C# version 2.0

Released November 2005

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# began as a generic Object-Oriented (OO) language, C# version 2.0 changed that in a hurry. 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 that 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.

C# version 1.2

Released April 2003

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 1.0

Released January 2002

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:

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