Language-Version-History.md

Features Added in C# Language Versions

C# 13.0 - .NET 9 and Visual Studio 2022 version 17.12

• ESC escape sequence: introduces the \e escape sequence to represent the ESCAPE/ESC character (U+001B).
• Method group natural type improvements: look scope-by-scope and prune inapplicable candidates early when determining the natural type of a method group.
• Lock object: allow performing a lock on System.Threading.Lock instances.
• Implicit indexer access in object initializers: allows indexers in object initializers to use implicit Index/Range indexers (new C { [^1] = 2 }).
• params collections: extends params support to collection types (void M(params ReadOnlySpan<int> s)).
• ref/unsafe in iterators/async: allows using ref/ref struct locals and unsafe blocks in iterators and async methods between suspension points.
• ref struct interfaces: allows ref struct types to implement interfaces and introduces the allows ref struct constraint.
• Overload resolution priority: allows API authors to adjust the relative priority of overloads within a type using System.Runtime.CompilerServices.OverloadResolutionPriority.
• Partial properties: allows splitting a property into multiple parts using the partial modifier.
• Better conversion from collection expression element: improves overload resolution to account for the element type of collection expressions.

C# 12.0 - .NET 8 and Visual Studio 2022 version 17.8

• Collection expressions: provides a uniform and efficient way of creating collections using collection-like types (List<int> list = [1, 2, 3];)
• Primary Constructors: helps reduce field and constructor boilerplate (class Point(int x, int y);)
• Inline Arrays: provides a general-purpose and safe mechanism for declaring arrays using the [InlineArray(size)] attribute.
• Using aliases for any type: relaxes many restrictions on using alias declarations, allowing built-in types, tuple types, pointer types, array types (using Point = (int x, int y);)
• Ref readonly parameters: ref readonly parameters mandate that arguments are passed by reference instead of potentially copied, can’t be modified, and warn if a temporary variable must be created.
• Nameof accessing instance members: relaxes some restrictions on usage of instance members inside nameof (nameof(field.ToString))
• Lambda optional parameters: allows lambda parameters to declare default values ((int i = 42) => { })

C# 11.0 - .NET 7 and Visual Studio 2022 version 17.4

• Raw string literals: introduces a string literal where the content never needs escaping (var json = """{ "summary": "text" }"""; or var json = $$"""{ "summary": "text", "length": {{length}} }""";).
• UTF-8 string literals: UTF-8 string literals with the u8 suffix (ReadOnlySpan<byte> s = "hello"u8;)
• Pattern match Span<char> on a constant string: an input value of type Span<char> or ReadonlySpan<char> can be matched with a constant string pattern (span is "123").
• Newlines in interpolations: allows newline characters in single-line interpolated strings.
• List patterns: allows matching indexable types (list is [1, 2, ..]).
• File-local types: introduces the file type modifier (file class C { ... }).
• Ref fields: allows ref field declarations in a ref struct (ref struct S { ref int field; ... }), introduces scoped modifier and [UnscopedRef] attribute.
• Required members: introduces the required field and property modifier and [SetsRequiredMembers] attribute.
• Static abstract members in interfaces: allows an interface to specify abstract static members.
• Unsigned right-shift operator: introduces the >>> operator and >>>=.
• checked user-defined operators: numeric and conversion operators support defining checked variants (public static Int128 operator checked +(Int128 lhs, Int128 rhs) { ... }).
• Relaxing shift operator requirements: the right-hand-side operand of a shift operator is no longer restricted to only be int
• Numeric IntPtr: nint/nuint become simple types aliasing System.IntPtr/System.UIntPtr.
• Auto-default structs: struct constructors automatically default fields that are not explicitly assigned.
• Generic attributes: allows attributes to be generic ([MyAttribute<int>]).
• Extended nameof scope in attributes: allows nameof(parameter) inside an attribute on a method or parameter ([MyAttribute(nameof(parameter))] void M(int parameter) { }).

C# 10.0 - .NET 6 and Visual Studio 2022 version 17.0

• Record structs (record struct Point(int X, int Y);, var newPoint = point with { X = 100 };).
• With expression on structs and anonymous types.
• Global using directives: global using directives avoid repeating the same using directives across many files in your program.
• Improved definite assignment: definite assignment and nullability analysis better handle common patterns such as dictionary?.TryGetValue(key, out value) == true.
• Constant interpolated strings: interpolated strings composed of constants are themselves constants.
• Extended property patterns: property patterns allow accessing nested members (if (e is MethodCallExpression { Method.Name: "MethodName" })).
• Sealed record ToString: a record can inherit a base record with a sealed ToString.
• Incremental source generators: improve the source generation experience in large projects by breaking down the source generation pipeline and caching intermediate results.
• Mixed deconstructions: deconstruction-assignments and deconstruction-declarations can be blended together ((existingLocal, var declaredLocal) = expression).
• Method-level AsyncMethodBuilder: the AsyncMethodBuilder used to compile an async method can be overridden locally.
• #line span directive: allow source generators like Razor fine-grained control of the line mapping with #line directives that specify the destination span (#line (startLine, startChar) - (endLine, endChar) charOffset "fileName").
• Lambda improvements: attributes and return types are allowed on lambdas; lambdas and method groups have a natural delegate type (var f = short () => 1;).
• Interpolated string handlers: interpolated string handler types allow efficient formatting of interpolated strings in assignments and invocations.
• File-scoped namespaces: files with a single namespace don't need extra braces or indentation (namespace X.Y.Z;).
• Parameterless struct constructors: support parameterless constructors and instance field initializers for struct types.
• CallerArgumentExpression: this attribute allows capturing the expressions passed to a method as strings.

C# 9.0 - .NET 5 and Visual Studio 2019 version 16.8

• Records and with expressions: succinctly declare reference types with value semantics (record Point(int X, int Y);, var newPoint = point with { X = 100 };).
• Init-only setters: init-only properties can be set during object creation (int Property { get; init; }).
• Top-level statements: the entry point logic of a program can be written without declaring an explicit type or Main method.
• Pattern matching enhancements: relational patterns (is < 30), combinator patterns (is >= 0 and <= 100, case 3 or 4:, is not null), parenthesized patterns (is int and (< 0 or > 100)), type patterns (case Type:).
• Native sized integers: the numeric types nint and nuint match the platform memory size.
• Function pointers: enable high-performance code leveraging IL instructions ldftn and calli (delegate* <int, void> local;)
• Suppress emitting localsinit flag: attributing a method with [SkipLocalsInit] will suppress emitting the localsinit flag to reduce cost of zero-initialization.
• Target-typed new expressions: Point p = new(42, 43);.
• Static anonymous functions: ensure that anonymous functions don't capture this or local variables (static () => { ... };).
• Target-typed conditional expressions: conditional expressions which lack a natural type can be target-typed (int? x = b ? 1 : null;).
• Covariant return types: a method override on reference types can declare a more derived return type.
• Lambda discard parameters: multiple parameters _ appearing in a lambda are allowed and are discards.
• Attributes on local functions.
• Module initializers: a method attributed with [ModuleInitializer] will be executed before any other code in the assembly.
• Extension GetEnumerator: an extension GetEnumerator method can be used in a foreach.
• Partial methods with returned values: partial methods can have any accessibility, return a type other than void and use out parameters, but must be implemented.
• Source Generators

C# 8.0 - .NET Core 3.0 and Visual Studio 2019 version 16.3

• Nullable reference types: express nullability intent on reference types with ?, notnull constraint and annotations attributes in APIs, the compiler will use those to try and detect possible null values being dereferenced or passed to unsuitable APIs.
• Default interface members: interfaces can now have members with default implementations, as well as static/private/protected/internal members except for state (ie. no fields).
• Recursive patterns: positional and property patterns allow testing deeper into an object, and switch expressions allow for testing multiple patterns and producing corresponding results in a compact fashion.
• Async streams: await foreach and await using allow for asynchronous enumeration and disposal of IAsyncEnumerable<T> collections and IAsyncDisposable resources, and async-iterator methods allow convenient implementation of such asynchronous streams.
• Enhanced using: a using declaration is added with an implicit scope and using statements and declarations allow disposal of ref structs using a pattern.
• Ranges and indexes: the i..j syntax allows constructing System.Range instances, the ^k syntax allows constructing System.Index instances, and those can be used to index/slice collections.
• Null-coalescing assignment: ??= allows conditionally assigning when the value is null.
• Static local functions: local functions modified with static cannot capture this or local variables, and local function parameters now shadow locals in parent scopes.
• Unmanaged generic structs: generic struct types that only have unmanaged fields are now considered unmanaged (ie. they satisfy the unmanaged constraint).
• Readonly members: individual members can now be marked as readonly to indicate and enforce that they do not modify instance state.
• Stackalloc in nested contexts: stackalloc expressions are now allowed in more expression contexts.
• Alternative interpolated verbatim strings: @$"..." strings are recognized as interpolated verbatim strings just like $@"...".
• Obsolete on property accessors: property accessors can now be individually marked as obsolete.
• Permit t is null on unconstrained type parameter

C# 7.3 - Visual Studio 2017 version 15.7

• System.Enum, System.Delegate and unmanaged constraints.
• Ref local re-assignment: Ref locals and ref parameters can now be reassigned with the ref assignment operator (= ref).
• Stackalloc initializers: Stack-allocated arrays can now be initialized, e.g. Span<int> x = stackalloc[] { 1, 2, 3 };.
• Indexing movable fixed buffers: Fixed buffers can be indexed into without first being pinned.
• Custom fixed statement: Types that implement a suitable GetPinnableReference can be used in a fixed statement.
• Improved overload candidates: Some overload resolution candidates can be ruled out early, thus reducing ambiguities.
• Expression variables in initializers and queries: Expression variables like out var and pattern variables are allowed in field initializers, constructor initializers and LINQ queries.
• Tuple comparison: Tuples can now be compared with == and !=.
• Attributes on backing fields: Allows [field: …] attributes on an auto-implemented property to target its backing field.

C# 7.2 - Visual Studio 2017 version 15.5

• Span and ref-like types
• In parameters and readonly references
• Ref conditional
• Non-trailing named arguments
• Private protected accessibility
• Digit separator after base specifier

C# 7.1 - Visual Studio 2017 version 15.3

• Async main
• Default expressions
• Reference assemblies
• Inferred tuple element names
• Pattern-matching with generics

C# 7.0 - Visual Studio 2017

• Out variables
• Pattern matching
• Tuples
• Deconstruction
• Discards
• Local Functions
• Binary Literals
• Digit Separators
• Ref returns and locals
• Generalized async return types
• More expression-bodied members
• Throw expressions

C# 6 - Visual Studio 2015

• Draft Specification online
• Compiler-as-a-service (Roslyn)
• Import of static type members into namespace
• Exception filters
• Await in catch/finally blocks
• Auto property initializers
• Default values for getter-only properties
• Expression-bodied members
• Null propagator (null-conditional operator, succinct null checking)
• String interpolation
• nameof operator
• Dictionary initializer

C# 5 - Visual Studio 2012

• Asynchronous methods
• Caller info attributes
• foreach loop was changed to generates a new loop variable rather than closing over the same variable every time

C# 4 - Visual Studio 2010

• Dynamic binding
• Named and optional arguments
• Co- and Contra-variance for generic delegates and interfaces
• Embedded interop types ("NoPIA")

C# 3 - Visual Studio 2008

• Implicitly typed local variables
• Object and collection initializers
• Auto-Implemented properties
• Anonymous types
• Extension methods
• Query expressions, a.k.a LINQ (Language Integrated Query)
• Lambda expression
• Expression trees
• Partial methods
• Lock statement

C# 2 - Visual Studio 2005

• Generics
• Partial types
• Anonymous methods
• Iterators, a.k.a yield statement
• Nullable types
• Getter/setter separate accessibility
• Method group conversions (delegates)
• Static classes
• Delegate inference
• Type and namespace aliases
• Covariance and contravariance

C# 1.2 - Visual Studio .NET 2003

• Dispose in foreach
• foreach over string specialization

C# 1.0 - Visual Studio .NET 2002

• Classes
• Structs
• Enums
• Interfaces
• Events
• Operator overloading
• User-defined conversion operators
• Properties
• Indexers
• Output parameters (out and ref)
• params arrays
• Delegates
• Expressions
• using statement
• goto statement
• Preprocessor directives
• Unsafe code and pointers
• Attributes
• Literals
• Verbatim identifier
• Unsigned integer types
• Boxing and unboxing