Appendix C - C# Version Features

This appendix provides a comprehensive index of C# features organized by version, with links to the relevant sections in the documentation where each feature is covered in detail.

C# 8.0 (2019)

Feature	Description	Documentation Link
Readonly Members	Add readonly modifier to struct members	Section 3.4.3 - Readonly Fields
Default Interface Methods	Interfaces can now have method implementations	Section 3.5.5 - Default Interface Methods (C# 8+)
Pattern Matching Enhancements	Switch expressions, property patterns, tuple patterns	Section 7.2.9 - Pattern Matching Enhancements (C# 9+)
Using Declarations	Simplified using statement without braces	Section 7.1.5 - Using using Statements
Static Local Functions	Local functions that can't capture local variables	Section 3.1.4 - Methods and Parameters
Nullable Reference Types	Explicit annotation for nullable references	Section 2.3.2.4 - Nullable Type Conversions
Asynchronous Streams	IAsyncEnumerable&lt;T&gt; for async iteration	Section 7.3.7 - Asynchronous Streams with IAsyncEnumerable<T>
Indices and Ranges	New syntax for accessing arrays and collections	Section 2.5.4.1 - System.Array Methods

C# 9.0 (2020)

Feature	Description	Documentation Link
Record Types	Reference types with value-based equality	Section 7.2.11 - Record Types (C# 9+)
Init-only Properties	Properties that can only be set during initialization	Section 7.2.10 - Init-only Properties (C# 9+)
Top-level Statements	Code without explicit Program class and Main method	Section 2.1.1 - C# Language Characteristics
Pattern Matching Enhancements	Type patterns, relational patterns, logical patterns	Section 7.2.9 - Pattern Matching Enhancements (C# 9+)
Target-typed New Expressions	Omit type in object creation when type is known	Section 3.1.2 - Creating and Using Objects
Covariant Return Types	Override methods can return more derived types	Section 3.6.6 - Covariance and Contravariance
Extension GetEnumerator	foreach can use extension GetEnumerator methods	Section 3.6.2 - Extension Methods
Lambda Discard Parameters	Use _ for unused lambda parameters	Section 7.2.2 - Lambda Expressions
Native Integers	nint and nuint types for platform-specific integers	Section 2.2.1 - Simple Types

C# 10.0 (2021)

Feature	Description	Documentation Link
Record Structs	Value type records	Section 7.2.11.2 - Record Classes vs. Record Structs (C# 10+)
Global Using Directives	Import namespaces for all files	Section 7.2.12 - Global Using Directives (C# 10+)
File-scoped Namespaces	Simplified namespace declarations	Section 7.2.13 - File-scoped Namespaces (C# 10+)
Extended Property Patterns	Nested property patterns	Section 7.2.9 - Pattern Matching Enhancements (C# 9+)
Constant Interpolated Strings	const strings with interpolation	Section 4.4.4 - String Interpolation
Lambda Improvements	Natural type for lambdas, attributes	Section 7.2.2 - Lambda Expressions
DateOnly and TimeOnly	Date and time without the overhead of DateTime	Section 4.6.5 - DateOnly and TimeOnly (C# 10+)

C# 11.0 (2022)

Feature	Description	Documentation Link
Required Members	Properties that must be initialized	Section 7.2.14 - Required Members (C# 11+)
Raw String Literals	Multi-line strings with improved formatting	Section 7.2.15 - Raw String Literals (C# 11+)
List Patterns	Pattern matching with lists and arrays	Section 7.2.9.5 - List Patterns (C# 11+)
Auto-Default Structs	Structs can be created without initializing all fields	Section 2.2.2 - Complex Types
Generic Attributes	Attributes can have type parameters	Section 7.2.3 - Reflection and Attributes
UTF-8 String Literals	String literals with UTF-8 encoding	Section 4.4.1 - String Creation and Manipulation
Pattern Matching on ReadOnlySpan	Use patterns with spans	Section 7.2.9 - Pattern Matching Enhancements (C# 9+)

C# 12.0 (2023)

Feature	Description	Documentation Link
Primary Constructors	Constructor parameters in class declaration	Section 7.2.17 - Primary Constructors (C# 12+)
Collection Expressions	Simplified collection initialization	Section 7.2.16 - Collection Expressions (C# 12+)
Inline Arrays	Fixed-size arrays as value types	Section 2.5.1.1 - Definition and Declaration
Optional Parameters in Lambda Expressions	Default values for lambda parameters	Section 7.2.2 - Lambda Expressions
ref readonly Parameters	Parameters that are references but can't be modified	Section 3.1.4 - Methods and Parameters
Alias Any Type	using directive can alias any type	Section 2.1.1 - C# Language Characteristics

C# 13.0 (2024)

Feature	Description	Documentation Link
Interceptors	Intercept method calls at compile time	Section 7.2.18 - Interceptors (C# 13)
Collection Expressions Enhancements	More collection types support	Section 7.2.16 - Collection Expressions (C# 12+)
Semi-auto Properties	Properties with custom backing fields	Section 3.1.8 - Properties with Backing Fields
params Collections	Support for params with collection types beyond arrays	Section 7.2.19 - Params Collections (C# 13)
New lock Type and Semantics	Enhanced thread synchronization with System.Threading.Lock	Section 7.3.10 - Thread Synchronization with Lock Type (C# 13+)
Partial Properties and Indexers	Support for partial properties and indexers in partial types	Section 3.1.14 - Partial Members (C# 13+)
ref struct Interfaces	Allow ref struct types to implement interfaces	Section 3.5.6 - Ref Struct Interfaces (C# 13+)
field Keyword	Access synthesized backing fields in property accessors	Section 3.1.8 - Properties with Backing Fields

C# 14.0 (2025)

Feature	Description	Documentation Link
Extension Members	Enhanced extension methods and new extension properties	Section 7.2.20 - Extension Members (C# 14)
Null-conditional Assignment	Use null-conditional operators on the left side of assignments	Section 7.2.21 - Null-conditional Assignment (C# 14)
nameof with Unbound Generic Types	Use nameof with open generic types	Section 7.2.22 - Nameof Enhancements (C# 14)
Implicit Span<T> Conversions	More implicit conversions for Span<T> and ReadOnlySpan<T>	Section 7.2.23 - Span Conversions (C# 14)
Lambda Parameters with Modifiers	Add modifiers to lambda parameters without specifying types	Section 7.2.2 - Lambda Expressions
field Backed Properties	Use field keyword to access synthesized backing fields	Section 3.1.8 - Properties with Backing Fields
Partial Events and Constructors	Support for partial events and constructors in partial types	Section 3.1.14.3 - Partial Events and Constructors (C# 14+)

Evolution of C# Features

Object-Oriented Programming

The evolution of object-oriented features in C#:

1. C# 8.0: Default interface methods, readonly members
2. C# 9.0: Records, init-only properties, covariant return types
3. C# 10.0: Record structs, parameterless struct constructors
4. C# 11.0: Required members, auto-default structs
5. C# 12.0: Primary constructors
6. C# 13.0: Semi-auto properties, partial properties and indexers, ref struct interfaces
7. C# 14.0: Extension properties, field backed properties, partial events and constructors

Functional Programming

The evolution of functional programming features in C#:

1. C# 8.0: Enhanced pattern matching, using declarations
2. C# 9.0: Top-level statements, improved pattern matching
3. C# 10.0: Lambda improvements, extended property patterns
4. C# 11.0: List patterns
5. C# 12.0: Collection expressions
6. C# 13.0: Interceptors, params collections
7. C# 14.0: Extension members, null-conditional assignment, lambda parameters with modifiers

Asynchronous Programming

The evolution of asynchronous programming features in C#:

1. C# 5.0: async/await
2. C# 8.0: Asynchronous streams (IAsyncEnumerable<T>)
3. C# 9.0: Improved async pattern matching
4. C# 10.0: AsyncMethodBuilder override
5. C# 13.0: Ref locals and unsafe contexts in async methods

Recommended Learning Path

For developers new to C#, we recommend learning the features in this order:

1. Core Language Features (C# 1-5): Classes, methods, properties, generics, LINQ, async/await
2. Modern Syntax Improvements (C# 6-8): String interpolation, null-conditional operators, pattern matching
3. Immutability Features (C# 9+): Records, init-only properties, required members
4. Latest Productivity Features (C# 10-12): Global usings, file-scoped namespaces, primary constructors, collection expressions
5. Advanced Language Features (C# 13-14): Interceptors, extension members, params collections, field keyword

Further Resources

• What's new in C# (Microsoft Docs)
• C# Language Versioning (Microsoft Docs)
• C# Language Design (GitHub)
• Breaking Changes in C# (Microsoft Docs)