C# Language Design

• 语言规范：https://github.com/dotnet/csharplang
• 最新特性：https://github.com/dotnet/roslyn/blob/master/docs/Language%20Feature%20Status.md
• 历史特性：https://github.com/dotnet/csharplang/blob/master/Language-Version-History.md

C# Language Specification

Standard ECMA-334

• December 2002，包含C# 1.0，C# 1.1，C# 1.2。
• June 2006，包含C# 2.0。
• December 2017，C# 5.0版本，最新版本。
• 除此之外其他版本（如C# 3.0，C#4.0，C#8.0等）未收入ECMA标准。

Microsoft

C# Language Feature

C# 1.0 - Visual Studio .NET 2002

• Classes
• Structs
• Interfaces
• Events
• Properties
• Delegates
• Expressions
• Statements
• Attributes
• Literals

C# 1.2 - Visual Studio .NET 2003

• Dispose in foreach
• foreach over string specialization

C# 2.0 - Visual Studio 2005

• Generics
• Partial types
• Anonymous methods
• Iterators
• Nullable types
• Getter/setter separate accessibility
• Method group conversions (delegates)
• Static classes
• Delegate inference

C# 3.0 - Visual Studio 2008

• Implicitly typed local variables
• Object and collection initializers
• Auto-Implemented properties
• Anonymous types
• Extension methods
• Query expressions
• Lambda expression
• Expression trees
• Partial methods

C# 4.0 - Visual Studio 2010

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

C# 5.0 - 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# 6.0 - 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# 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# 7.1 - Visual Studio 2017 version 15.3

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

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# 7.3 - 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 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# 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 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# 9.0

Reference

• C# 语言历史版本特性（C# 1.0到C# 7.3汇总更新-2018.5更新）
• C# 发展历史
• C# 9.0新特性

C# 版本特性（1.0 - 9.0）详细介绍