Every feature is tagged with what it is for rather than which version it arrived in. Use this when you know the kind of problem you have - "this allocation is in a hot loop" - rather than the release you need to target.

All 158 feature pages are tagged, and most carry more than one tag, so a feature can appear under several headings.

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• Code reduction (66)
• Readability (43)
• Correctness (35)
• Performance (30)
• New scenarios (17)
• Type safety (15)
• Code generation (7)
• Interop (6)
• Discovery (4)
• Extensibility (3)
• Concurrency (1)

Code reduction

Features that remove boilerplate you had to write before.

• Anonymous methods C# 2.0 - Create a delegate using an inline function body.
• Delegate covariance and contravariance C# 2.0 - Allow a delegate to point at a method whose parameters or return type are less or more derived than the delegate's signature.
• Null-coalescing operator C# 2.0 - Provide a default value when an expression is null.
• Anonymous types C# 3.0 - Create objects without explicitly defining a type.
• Auto implemented properties C# 3.0 - Declare properties without explicit backing fields.
• Collection initializers C# 3.0 - Populate collections inline during construction.
• Implicitly typed local variables C# 3.0 - Declare variables with var so the compiler infers the type.
• Object initializers C# 3.0 - Set property values when creating an object.
• Optional arguments C# 4.0 - Define default values for method parameters to make them optional.
• Caller info attributes C# 5.0 - Provide parameter attributes to capture information about the caller of a method.
• Auto property initializer C# 6.0 - Allow auto-implemented properties to have an initial value.
• Expression bodied members C# 6.0 - Declare members using => arrow functions.
• Index initializers C# 6.0 - Allow indexers to be set from object or collection initializers.
• Null-conditional operators C# 6.0 - Safely access members on potentially null objects.
• String interpolation C# 6.0 - Build formatted strings with in-place evaluation.
• using static C# 6.0 - Import static members as top-level functions.
• Deconstruction C# 7.0 - Extract tuple and property values from objects.
• Expanded expression bodied members C# 7.0 - Allow the => syntax for constructors, finalizers, and get/set accessors.
• Out variables C# 7.0 - Declare out parameters inline.
• Pattern matching C# 7.0 - Pattern match expressions for type and value checking.
• Throw expressions C# 7.0 - Throw exceptions in more convenient ways.
• Tuples C# 7.0 - Group multiple values without creating a dedicated type.
• Async main C# 7.1 - Use async and await directly in Program.Main.
• Default literals C# 7.1 - Use default without specifying the type explicitly.
• Generic type pattern matching C# 7.1 - Use pattern matching with generic type constraints.
• Inferred tuple element names C# 7.1 - Infer tuple element names from variable names.
• Conditional ref expressions C# 7.2 - Use the conditional operator with ref returns and ref locals.
• Non-trailing named arguments C# 7.2 - Use named arguments in any position when positional arguments follow.
• Expression variables in initializers C# 7.3 - Use out var and pattern variables in field initializers, constructor initializers, and LINQ queries.
• Ref reassignment C# 7.3 - Point an existing ref local or ref parameter at a different variable.
• Stackalloc array initializers C# 7.3 - Initialize stackalloc arrays with inline values.
• Tuple equality operators C# 7.3 - Compare tuples directly using == and != operators.
• Null coalescing assignment C# 8.0 - A short syntax for assigning a value to an object if it is null.
• Property pattern C# 8.0 - Match against object properties within pattern matching expressions.
• Ranges and indices C# 8.0 - Use .. and ^ operators to slice collections and access elements from the end.
• Recursive pattern matching C# 8.0 - Match against properties and nested object structures in patterns.
• stackalloc in nested expressions C# 8.0 - Allow a stackalloc expression anywhere an expression is permitted, not just as a direct initializer.
• Switch expressions C# 8.0 - A switch designed to return values directly within a method.
• Switch tuple pattern C# 8.0 - Match against multiple values simultaneously using tuple patterns.
• Using declarations C# 8.0 - Simplify disposable resource management without nesting.
• Pattern matching improvements C# 9.0 - Enhanced pattern matching with relational, logical, and simplified type patterns.
• Records C# 9.0 - Declare immutable types and eliminate boilerplate code.
• Target-typed conditional expression C# 9.0 - Eliminate casts in conditional operations by considering the result type.
• Target-typed new C# 9.0 - Use new without a type if the compiler can infer it.
• Top-level statements C# 9.0 - Skip Program.Main() for a script-like experience.
• Caller argument expressions C# 10.0 - Allow methods to capture the code passed in an argument at compile time.
• Constant interpolated strings C# 10.0 - Allow constant strings to use string interpolation.
• Extended property patterns C# 10.0 - Allow property sub-patterns to reference nested members.
• Lambda improvements C# 10.0 - Add attributes, explicit return types, and natural type inference to lambdas.
• Parameterless struct constructors C# 10.0 - Allow structs to have parameterless constructors.
• Record structs C# 10.0 - Allow records to be value type structs.
• with expressions for structs C# 10.0 - Create modified copies of structs and anonymous types using with expressions.
• Auto-default structs C# 11.0 - The compiler auto-initializes unassigned struct fields in constructors.
• List patterns C# 11.0 - Match arrays and lists against sequences of patterns.
• Raw string literals C# 11.0 - Allow strings containing newlines and quotes without escaping.
• Unsigned right shift operator C# 11.0 - Shift the bits of an integer to the right ignoring the sign.
• Alias any type C# 12.0 - Use the alias directive to give names to types like tuples.
• Collection expressions C# 12.0 - A short syntax for initializing collections.
• Default lambda parameters C# 12.0 - Allow a lambda's parameters to specify default values.
• Primary constructors C# 12.0 - Define a constructor and backing fields with a short syntax.
• Allow params to use collections C# 13.0 - The params keyword no longer has to use an array but can use other collection types.
• Field keyword C# 14.0 - Reference the synthesized backing field of an auto property using the field keyword.
• Implicit span conversions C# 14.0 - Implicitly convert arrays and strings to spans without explicit casting.
• Simple lambda parameters with modifiers C# 14.0 - Use parameter modifiers without specifying types in simple lambda syntax.
• Collection expression arguments C# 15.0 - Pass capacity, comparers and other constructor arguments from inside a collection expression.
• Labeled break and continue C# 15.0 - Break out of or continue an outer loop directly from inside nested loops.

Readability

Features that make the intent of existing code clearer.

• Delegate covariance and contravariance C# 2.0 - Allow a delegate to point at a method whose parameters or return type are less or more derived than the delegate's signature.
• Null-coalescing operator C# 2.0 - Provide a default value when an expression is null.
• Implicitly typed local variables C# 3.0 - Declare variables with var so the compiler infers the type.
• Lambda expressions C# 3.0 - Create inline functions using concise => arrow syntax.
• Object initializers C# 3.0 - Set property values when creating an object.
• Query expressions C# 3.0 - Provide a native query syntax reminiscent of SQL.
• Named arguments C# 4.0 - Specify method parameters by name instead of position.
• Asynchronous members C# 5.0 - Provide async and await operations to simplify Task-based operations.
• Exception filters C# 6.0 - Conditionally catch exceptions based on a boolean expression.
• String interpolation C# 6.0 - Build formatted strings with in-place evaluation.
• Binary literals C# 7.0 - Allow numeric literals to be written in binary.
• Digit separators C# 7.0 - Allow numeric literals to contain the _ character as a visual aid.
• Discards C# 7.0 - Signal that values are intentionally being ignored.
• Pattern matching C# 7.0 - Pattern match expressions for type and value checking.
• Throw expressions C# 7.0 - Throw exceptions in more convenient ways.
• Numeric literal leading underscores C# 7.2 - Allow underscores to be used before the first digit in a numeric literal.
• Tuple equality operators C# 7.3 - Compare tuples directly using == and != operators.
• Property pattern C# 8.0 - Match against object properties within pattern matching expressions.
• Ranges and indices C# 8.0 - Use .. and ^ operators to slice collections and access elements from the end.
• Switch expressions C# 8.0 - A switch designed to return values directly within a method.
• Switch tuple pattern C# 8.0 - Match against multiple values simultaneously using tuple patterns.
• Using declarations C# 8.0 - Simplify disposable resource management without nesting.
• Init-only setters C# 9.0 - Specify properties that can only be set during construction.
• Lambda discard parameters C# 9.0 - Signify no interest in a parameter to a lambda.
• Pattern matching improvements C# 9.0 - Enhanced pattern matching with relational, logical, and simplified type patterns.
• Target-typed new C# 9.0 - Use new without a type if the compiler can infer it.
• Constant interpolated strings C# 10.0 - Allow constant strings to use string interpolation.
• Extended property patterns C# 10.0 - Allow property sub-patterns to reference nested members.
• File-scoped namespaces C# 10.0 - Allow a namespace to be specified for an entire file to reduce indentation.
• global using directives C# 10.0 - Specify common using directives to be used across all source files.
• with expressions for structs C# 10.0 - Create modified copies of structs and anonymous types using with expressions.
• Extended nameof scope C# 11.0 - Use nameof with method parameters in attributes on that method.
• List patterns C# 11.0 - Match arrays and lists against sequences of patterns.
• Newlines in string interpolations C# 11.0 - Allow newlines inside interpolated string expression holes.
• Pattern match Span on string constants C# 11.0 - Use pattern matching to compare a Span of characters against a string literal.
• Raw string literals C# 11.0 - Allow strings containing newlines and quotes without escaping.
• Collection expressions C# 12.0 - A short syntax for initializing collections.
• Character literal escape sequence C# 13.0 - A new \e escape sequence for character literals.
• Implicit index access C# 13.0 - Allow the ^ from-end operator to be used in object initializers.
• Method group natural type improvements C# 13.0 - Method groups are now more likely to identify the correct method.
• Null-conditional assignment C# 14.0 - Conditionally assign values with ?. just like reading values.
• Extension indexers C# 15.0 - Add indexers to existing types from an extension block.
• Labeled break and continue C# 15.0 - Break out of or continue an outer loop directly from inside nested loops.

Correctness

Features that let the compiler catch a mistake you could previously make.

• Iterators C# 2.0 - Produce and consume sequences.
• Nullable value types C# 2.0 - Give value-types "null" semantics to indicate missing values.
• Pragma directives C# 2.0 - Use #pragma warning to selectively suppress or restore compiler warnings.
• Foreach variable capture fix C# 5.0 - Each iteration of foreach now captures its own copy of the loop variable.
• Exception filters C# 6.0 - Conditionally catch exceptions based on a boolean expression.
• nameof operator C# 6.0 - Capture the name of a variable, type or member at compile time.
• Discards C# 7.0 - Signal that values are intentionally being ignored.
• Local function statements C# 7.0 - Allow functions to be declared inside other functions.
• Out variables C# 7.0 - Declare out parameters inline.
• Pattern matching C# 7.0 - Pattern match expressions for type and value checking.
• In parameter modifiers C# 7.2 - Pass parameters by reference without allowing modifications.
• Private protected access modifier C# 7.2 - Restrict access to derived types within the same assembly.
• readonly struct C# 7.2 - Declare immutable value types that cannot be modified after creation.
• ref readonly method returns C# 7.2 - Return references that cannot be modified by the caller.
• Null-forgiving operator C# 8.0 - Suppress nullable reference type warnings when you know a value isn't null.
• Nullable reference types C# 8.0 - Allow use of reference types to be declared nullable or non-nullable.
• readonly instance members C# 8.0 - Allow struct members that do not modify state to be annotated as such.
• Static local functions C# 8.0 - Allow local functions to be declared static so they do not capture the class.
• Init-only setters C# 9.0 - Specify properties that can only be set during construction.
• Lambda discard parameters C# 9.0 - Signify no interest in a parameter to a lambda.
• Records C# 9.0 - Declare immutable types and eliminate boilerplate code.
• Checked user-defined operators C# 11.0 - Define checked versions of user-defined operators for overflow-aware arithmetic.
• Extended nameof scope C# 11.0 - Use nameof with method parameters in attributes on that method.
• Required members C# 11.0 - Require members to be set by initializers.
• Static interface members C# 11.0 - Allow members of an interface to be static abstract or virtual.
• Experimental attribute C# 12.0 - An annotation attribute to signal areas that are experimental.
• ref readonly parameters C# 12.0 - Allow parameters to be passed by reference without being modified.
• Character literal escape sequence C# 13.0 - A new \e escape sequence for character literals.
• Implicit index access C# 13.0 - Allow the ^ from-end operator to be used in object initializers.
• Method group natural type improvements C# 13.0 - Method groups are now more likely to identify the correct method.
• Field keyword C# 14.0 - Reference the synthesized backing field of an auto property using the field keyword.
• Unbound generic types and nameof C# 14.0 - Use the nameof keyword with generic definitions.
• Closed hierarchies C# 15.0 - Mark a class as closed so only types in its own assembly can derive from it, enabling exhaustive switches.
• Memory safety C# 15.0 - Pointer relaxations, requires-unsafe members and unsafe expressions tie unsafe to the operations that access memory.
• Union types C# 15.0 - Declare a type that holds exactly one of several case types, with exhaustive switch checking.

Performance

Features that avoid an allocation, a copy or a virtual call.

• Ref local variable C# 7.0 - Create a reference to the original value.
• Ref return C# 7.0 - Return references to variables instead of copies of values.
• In parameter modifiers C# 7.2 - Pass parameters by reference without allowing modifications.
• ref readonly method returns C# 7.2 - Return references that cannot be modified by the caller.
• ref struct C# 7.2 - Declare stack-only value types that cannot be allocated on the heap.
• Ref reassignment C# 7.3 - Point an existing ref local or ref parameter at a different variable.
• Stackalloc array initializers C# 7.3 - Initialize stackalloc arrays with inline values.
• Unmanaged generic type constraints C# 7.3 - Constrain generic types to unmanaged types only.
• Pattern-based using and disposable ref structs C# 8.0 - Support using statements for types that offer a Dispose method without implementing IDisposable.
• readonly instance members C# 8.0 - Allow struct members that do not modify state to be annotated as such.
• stackalloc in nested expressions C# 8.0 - Allow a stackalloc expression anywhere an expression is permitted, not just as a direct initializer.
• Static local functions C# 8.0 - Allow local functions to be declared static so they do not capture the class.
• Unmanaged constructed types C# 8.0 - Allow a generic type built from unmanaged type arguments to satisfy the unmanaged constraint.
• Function pointers C# 9.0 - Call methods through pointers without delegate allocations in performance-critical code.
• Skip locals init C# 9.0 - Prevent the CLR from zeroing local variables for performance.
• Static anonymous functions C# 9.0 - Prevent an anonymous function from capturing state.
• Interpolated string handlers C# 10.0 - Replace interpolated string expressions with handlers to optimize performance.
• Pattern match Span on string constants C# 11.0 - Use pattern matching to compare a Span of characters against a string literal.
• ref fields and scoped ref C# 11.0 - Allow ref fields inside ref struct types and control ref lifetime with scoped.
• Unsigned right shift operator C# 11.0 - Shift the bits of an integer to the right ignoring the sign.
• UTF-8 string literals C# 11.0 - Allow literal strings to be stored as UTF-8 instead of UTF-16.
• Inline arrays C# 12.0 - Annotate a struct with InlineArray for optimized performance.
• ref readonly parameters C# 12.0 - Allow parameters to be passed by reference without being modified.
• Allow params to use collections C# 13.0 - The params keyword no longer has to use an array but can use other collection types.
• allows ref struct C# 13.0 - Allow ref struct types to be used as generic type arguments.
• New lock object C# 13.0 - A new disposable System.Threading.Lock type optimized for modern lock statements.
• ref and unsafe in iterators and async C# 13.0 - Allow ref locals and unsafe blocks in iterator and async methods.
• Implicit span conversions C# 14.0 - Implicitly convert arrays and strings to spans without explicit casting.
• User-defined compound assignment C# 14.0 - Define custom behavior for compound assignment operators like += and -=.
• Collection expression arguments C# 15.0 - Pass capacity, comparers and other constructor arguments from inside a collection expression.

New scenarios

Features that make something possible that was not possible before.

• Expression trees C# 3.0 - Represent code as data structures for analysis or transformation.
• Lambda expressions C# 3.0 - Create inline functions using concise => arrow syntax.
• Dynamic binding C# 4.0 - Defer type checking until runtime using the dynamic keyword.
• Asynchronous members C# 5.0 - Provide async and await operations to simplify Task-based operations.
• Auto-implemented property field attributes C# 7.3 - Allow attributes to be applied to the hidden backing field of auto-implemented properties.
• Async streams C# 8.0 - Create and consume streams asynchronously.
• Pattern-based using and disposable ref structs C# 8.0 - Support using statements for types that offer a Dispose method without implementing IDisposable.
• Attributes on local functions C# 9.0 - Apply attributes to local functions and their parameters.
• Module initializers C# 9.0 - Run code in an assembly when it is first loaded.
• Native integers C# 9.0 - Provide architecture-specific integer types.
• ref fields and scoped ref C# 11.0 - Allow ref fields inside ref struct types and control ref lifetime with scoped.
• allows ref struct C# 13.0 - Allow ref struct types to be used as generic type arguments.
• ref and unsafe in iterators and async C# 13.0 - Allow ref locals and unsafe blocks in iterator and async methods.
• File-based app directives C# 14.0 - New preprocessor directives for configuring file-based apps.
• User-defined compound assignment C# 14.0 - Define custom behavior for compound assignment operators like += and -=.
• Closed hierarchies C# 15.0 - Mark a class as closed so only types in its own assembly can derive from it, enabling exhaustive switches.
• Union types C# 15.0 - Declare a type that holds exactly one of several case types, with exhaustive switch checking.

Type safety

Features that narrow what a type is allowed to hold.

• Friend assemblies C# 2.0 - Use InternalsVisibleTo to expose internal members to specific assemblies.
• Generics C# 2.0 - Write type-safe code that works with multiple data types.
• Nullable value types C# 2.0 - Give value-types "null" semantics to indicate missing values.
• Property accessor accessibility C# 2.0 - Specify different access modifiers on a property's get and set accessors.
• Static classes C# 2.0 - Declare a class as static to prevent instantiation and ensure only static members.
• Embedded interop types C# 4.0 - Embed COM interop type information directly into assemblies.
• Generic contravariant C# 4.0 - Mark a generic type parameter with in so a less derived type argument can be used.
• Generic covariant C# 4.0 - Mark a generic type parameter with out so a more derived type argument can be used.
• Enum and Delegate generic constraints C# 7.3 - Constrain generic type parameters to System.Enum or System.Delegate.
• Covariant returns C# 9.0 - Allow a method to return a more specific type than the method it overrides.
• Native integers C# 9.0 - Provide architecture-specific integer types.
• Checked user-defined operators C# 11.0 - Define checked versions of user-defined operators for overflow-aware arithmetic.
• Generic attributes C# 11.0 - Allow attributes to take generic type arguments for strong typing.
• Static interface members C# 11.0 - Allow members of an interface to be static abstract or virtual.
• Alias any type C# 12.0 - Use the alias directive to give names to types like tuples.

Code generation

Features aimed at generators and tooling rather than hand-written code.

• Partial types C# 2.0 - Split type definitions between files to separate generated and human-written code.
• Partial methods C# 3.0 - Define a method signature in a partial class for implementation elsewhere.
• Extending partial methods C# 9.0 - Partial methods can have return values and out parameters.
• File local types C# 11.0 - Restrict a type so it can only be referenced from the file it is declared in.
• Interceptors C# 12.0 - Allow a method to declare it replaces another method.
• Partial properties & indexers C# 13.0 - Allow properties and indexers to be partially defined like partial methods.
• Partial events and constructors C# 14.0 - Allow constructors and events to be partially defined like partial methods and properties.

Interop

Features for working with other languages, runtimes and platforms.

• Extern alias C# 2.0 - Disambiguate types with the same fully-qualified name from different assemblies.
• Dynamic binding C# 4.0 - Defer type checking until runtime using the dynamic keyword.
• Embedded interop types C# 4.0 - Embed COM interop type information directly into assemblies.
• Unmanaged constructed types C# 8.0 - Allow a generic type built from unmanaged type arguments to satisfy the unmanaged constraint.
• Function pointers C# 9.0 - Call methods through pointers without delegate allocations in performance-critical code.
• Memory safety C# 15.0 - Pointer relaxations, requires-unsafe members and unsafe expressions tie unsafe to the operations that access memory.

Discovery

Features that surface information from the compiler.

• Extension methods C# 3.0 - Add methods to existing types without modifying them.
• global using directives C# 10.0 - Specify common using directives to be used across all source files.
• Extension members C# 14.0 - Add properties to existing classes just like extension methods.
• Extension indexers C# 15.0 - Add indexers to existing types from an extension block.

Extensibility

Features for adding behaviour to types you do not own.

• Default interface methods C# 8.0 - Allow interfaces to evolve by providing default implementations of methods.
• Extension GetEnumerator C# 9.0 - Extension methods allow foreach to enumerate over new types.
• Overload resolution priority C# 13.0 - Allow library authors to guide which overload is preferred using an attribute.

Concurrency

Features that change how code runs in parallel.

• New lock object C# 13.0 - A new disposable System.Threading.Lock type optimized for modern lock statements.