C# Next (C# 12 후보) - slog

dimohy · March 18, 2023, 11:36pm

C# 12에 도입될 예정인 기능에 대해 살펴봅니다.

dotnet/roslyn/blob/main/docs/Language Feature Status.md

Language Feature Status
=====

This document reflects the status, and planned work in progress, for the compiler team.  It is a live document
and will be updated as work progresses, features are added / removed, and as work on feature progresses.
This is not an exhaustive list of our features but rather the ones which have active development
efforts behind them.

# C# Next

| Feature | Branch | State | Developer | Reviewer | LDM Champ |
| ------- | ------ | ----- | --------- | -------- | --------- |
| [Using aliases for any type](https://github.com/dotnet/csharplang/issues/4284) | [UsingAliasTypes](https://github.com/dotnet/roslyn/tree/features/UsingAliasTypes) | [Merged into 17.6.P3](https://github.com/dotnet/roslyn/issues/56323) | [CyrusNajmabadi](https://github.com/CyrusNajmabadi) | [jcouv](https://github.com/jcouv) [cston](https://github.com/cston) |  |
| [Primary Constructors](https://github.com/dotnet/csharplang/issues/2691) | [PrimaryConstructors](https://github.com/dotnet/roslyn/tree/features/PrimaryConstructors) | [Merged into 17.6.P2](https://github.com/dotnet/roslyn/issues/65697) | [AlekseyTs](https://github.com/AlekseyTs) | [cston](https://github.com/cston), [jjonescz](https://github.com/jjonescz) | [MadsTorgersen](https://github.com/MadsTorgersen) |
| [Semi-auto-properties](https://github.com/dotnet/csharplang/issues/140) | [semi-auto-props](https://github.com/dotnet/roslyn/tree/features/semi-auto-props) | [In Progress](https://github.com/dotnet/roslyn/issues/57012) | [Youssef1313](https://github.com/Youssef1313) | [333fred](https://github.com/333fred), [RikkiGibson](https://github.com/RikkiGibson) | [CyrusNajmabadi](https://github.com/CyrusNajmabadi) |
| [Params Span\<T> + Stackalloc any array type](https://github.com/dotnet/csharplang/issues/1757) | [params-span](https://github.com/dotnet/roslyn/tree/features/params-span) | [In Progress](https://github.com/dotnet/roslyn/issues/57049) | [cston](https://github.com/cston) | TBD | [jaredpar](https://github.com/jaredpar) |
| [nameof accessing instance members](https://github.com/dotnet/roslyn/issues/40229) | main | [In Progress](https://github.com/dotnet/roslyn/pull/48754) | [YairHalberstadt ](https://github.com/YairHalberstadt) | [333fred](https://github.com/333fred), [AlekseyTs](https://github.com/AlekseyTs)  | [333fred](https://github.com/333fred) |
| [Lambda default parameters](https://github.com/dotnet/csharplang/issues/6051) | [lambda-default-parameters](https://github.com/dotnet/roslyn/tree/features/lambda-default-parameters) | [Merged into 17.5p2](https://github.com/dotnet/roslyn/issues/62485) | [adamperlin](https://github.com/adamperlin), [jjonescz](https://github.com/jjonescz) | [333fred](https://github.com/333fred), [cston](https://github.com/cston)  | [captainsafia](https://github.com/captainsafia) | 
| [Default in deconstruction](https://github.com/dotnet/roslyn/pull/25562) | [decon-default](https://github.com/dotnet/roslyn/tree/features/decon-default) | [In Progress](https://github.com/dotnet/roslyn/issues/25559) | [jcouv](https://github.com/jcouv) | [gafter](https://github.com/gafter) | [jcouv](https://github.com/jcouv) |
| [Collection Literals](https://github.com/dotnet/csharplang/issues/5354) | [CollectionLiterals](https://github.com/dotnet/roslyn/tree/features/CollectionLiterals) | [In Progress](https://github.com/dotnet/roslyn/issues/66418) | [cston](https://github.com/cston) | [333fred](https://github.com/333fred), [RikkiGibson](https://github.com/RikkiGibson) | [CyrusNajmabadi](https://github.com/CyrusNajmabadi) |

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기능이 구현되었을 때마다 내용을 살펴보도록 하겠습니다.

dimohy · March 18, 2023, 11:50pm

모든 유형에 별칭 사용 (구현됨, 17.6 P3에 반영)

C# 12은 이제 다음의 코드가 합법입니다.

using Point = (int X, int Y);

github.com

dotnet/csharplang/blob/main/proposals/using-alias-types.md

# Allow using alias directive to reference any kind of Type

## Summary
Relax the using_alias_directive ([§13.5.2](https://github.com/dotnet/csharpstandard/blob/draft-v6/standard/namespaces.md#1352-using-alias-directives)) to allow it to point at any sort of type, not just named types.  This would support types not allowed today, like: tuple types, pointer types, array types, etc.  For example, this would now be allowed:

```c#
using Point = (int x, int y);
```

## Motivation
For ages, C# has had the ability to introduce aliases for namespaces and named types (classes, delegated, interfaces, records and structs).  This worked acceptably well as it provided a means to introduce non-conflicting names in cases where a normal named pulled in from `using_directive`s might be ambiguous, and it allowed a way to provide a simpler name when dealing with complex generic types.  However, the rise of additional complex type symbols in the language has caused more use to arise where aliases would be valuable but are currently not allowed.  For example, both tuples and function-pointers often can have large and complex regular textual forms that can be painful to continually write out, and a burden to try to read.  Aliases would help in these cases by giving a short, developer-provided, name that can then be used in place of those full structural forms.

## Detailed design
We will change the grammar of `using_alias_directive` thusly:

```
using_alias_directive
-    : 'using' identifier '=' namespace_or_type_name ';'
+    : 'using' identifier '=' (namespace_name | type) ';'
    ;

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dimohy · March 19, 2023, 12:08am

기본 생성자 (구현됨, 17.6 P2에 반영)

C# 12은 이제 다음의 코드와 같이 class, struct에서 생성자 매개변수를 지정할 수 있으며 내부에서 사용할 경우 적절하게 private 필드로 캡쳐 됩니다.

class TestClass(int x, int y);

record와 다른 점은 x와 y가 외부로 노출되지 않는다는 점입니다.

Visual Studio의 최신 미리보기 빌드로 csporj에 다음의 설정을 한 후 확인이 가능합니다.

<PropertyGroup>
   <LangVersion>Preview</LangVersion>
</PropertyGroup>

github.com

dotnet/csharplang/blob/main/proposals/primary-constructors.md

# Primary constructors

## Summary
[summary]: #summary

Classes and structs can have a parameter list, and their base class specification can have an argument list.
Primary constructor parameters are in scope throughout the class or struct declaration, and if they are captured by a function member or anonymous function, they are appropriately stored (e.g. as unspeakable private fields of the declared class or struct).

The proposal "retcons" the primary constructors already available on records in terms of this more general feature with some additional members synthesized.

## Motivation
[motivation]: #motivation

The ability of a class or struct in C# to have more than one constructor provides for generality, but at the expense of some tedium in the declaration syntax, because the constructor input and the class state need to be cleanly separated.

Primary constructors put the parameters of one constructor in scope for the whole class or struct to be used for initialization or directly as object state. The trade-off is that any other constructors must call through the primary constructor.

``` c#
public class C(bool b, int i, string s) : B(b) // b passed to base constructor
{

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dimohy · March 19, 2023, 12:11am

람다 기본 매개변수 (구현됨, 17.5 P2에 반영)

C# 12에서는 이제 람다에서 기본 매개변수를 사용할 수 있습니다.

var addWithDefault = (int addTo = 2) => addTo + 1;
addWithDefault(); // 3
addWithDefault(5); // 6

github.com

dotnet/csharplang/blob/main/proposals/lambda-method-group-defaults.md

# Optional and parameter array parameters for lambdas and method groups

## Summary

[summary]: #summary

To build on top of the lambda improvements introduced in C# 10 (see [relevant background](#relevant-background)), we propose adding support for default parameter values and `params` arrays in lambdas. This would enable users to implement the following lambdas:

```csharp
var addWithDefault = (int addTo = 2) => addTo + 1;
addWithDefault(); // 3
addWithDefault(5); // 6

var counter = (params int[] xs) => xs.Length;
counter(); // 0
counter(1, 2, 3); // 3
```

Similarly, we will allow the same kind of behavior for method groups:
```csharp

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dimohy · March 28, 2023, 1:15pm

dimohy · April 12, 2023, 1:41am

Visual Studio 2022 17.6 P3이 출시되면서 이제 미리보기로 확인할 수 있습니다.

  <PropertyGroup>
    <LangVersion>preview</LangVersion>
  </PropertyGroup>

using Point = (int X, int Y);

Point x = (10, 15);
Point y = (20, 12);

var z = new Point(x.X + y.X, x.Y + y.Y);

Console.WriteLine(z);

dimohy · April 12, 2023, 2:51am

dimohy · April 14, 2023, 1:32am

C#12 클래스 및 구조체 기본 생성자 | Patrick Smacchia 👓 읽을 거리

본 글은 NDepend의 Patrick Smacchia님의 C#12 class and struct Primary Constructors를 번역하였습니다. [image] C# 9부터는 class record(또는 그냥 record)와 struct record 편리한 기본 생성자 구문이 있습니다. var p = new Person("Seth", "Gecko"); Assert.IsTrue($"{p.FirstName} {p.LastName}" == "Seth Gecko"); // p.FirstName = "Alan"; ERROR record are immutable by default public record Person(string FirstName, string LastName); C# 12는 비 레코드인 class와 struct에 대한 기본 생성자를 도입했지만 매우 다르다는 점에 유의하세요! 근본적인 동기가 다르기 때문입니다. record 기본 생성자는 공용 읽…

dimohy · April 18, 2023, 12:49pm

인스턴스 이름에 nameof 접근 (구현됨, 17.7 P1에 반영)

using System;
public struct C {
    public string P;
    public static string M1() => nameof(P); // Legal
    public static string M2() => nameof(P.Length); // error CS0120: An object reference is required for the non-static field, method, or property 'C.P'
}

위의 코드와 같이 정적 컨텍스트에서 인스턴스 멤버에 엑세스 할 경우 컴파일 오류가 발생하는 경우가 있습니다.

17.7 P1 이후 부터는 이 컴파일 오류는 발생하지 않습니다.

dimohy · April 20, 2023, 11:02pm

dimohy · May 5, 2023, 11:44pm

dimohy · May 11, 2023, 11:25pm

https://www.sysnet.pe.kr/2/0/13338

dimohy · May 11, 2023, 11:26pm

https://www.sysnet.pe.kr/2/0/13339

dimohy · May 11, 2023, 11:26pm

https://www.sysnet.pe.kr/2/0/13341

dimohy · May 17, 2023, 1:07am

VS 17.7p1이 릴리스 되면서 개선된 기능을 테스트할 수 있게 되었습니다. 이제 인스턴스 멤버도 nameof 대상으로 사용할 수 있습니다.

Console.WriteLine(C.M1());
Console.WriteLine(C.M2());


public struct C
{
    public string P;
    public static string M1() => nameof(P); // Legal
    public static string M2() => nameof(P.Length); // error CS0120: An object reference is required for the non-static field, method, or property 'C.P'
}

| 출력

P
Length

dimohy · July 12, 2023, 1:47am

dimohy · July 19, 2023, 12:44pm

C# 12의 기능이 거의 확정되었습니다. 꽤 많은 기능이 C# 12에서 제외된다는 사실이 약간 슬프네요.
특히 반자동 속성(Semi auto properties)의 경우 꽤 많이 사용할 기능이라 이전 버전부터 기다렸는데 의외로 구현이 어려운가 봅니다.

dimohy · July 20, 2023, 12:02pm

드디어 컬렉션 리터럴이 C#에 도입되는군요. 한마디로 이제 목록을 [1, 2, 3] 형태로 쓸 수 있게 됩니다.
사전 형식도 [key: value, …]로 사용할 수 있습니다.
단순히 중괄호에서 대괄호로 변경된것이 아니라 이전에는 목록을 사용하려면 new xx[] 로 해서 무조건 힙을 사용할 수 밖에 없거나 stackalloc으로 명시적 스택 할당을 해야 했다면 Span<T> 유형으로 받을 경우 작은 단위의 컬렉션은 암묵적으로 stackalloc을 사용하게 됩니다.

github.com

dotnet/csharplang/blob/main/proposals/collection-expressions.md#span-types

# Collection expressions

## Summary
[summary]: #summary

Collection expressions introduce a new terse syntax, `[e1, e2, e3, etc]`, to create common collection values.  Inlining other collections into these values is possible using a spread operator `..` like so: `[e1, ..c2, e2, ..c2]`.  A `[k1: v1, ..d1]` form is also supported for creating dictionaries.

Several collection-like types can be created without requiring external BCL support.  These types are:
* [Array types](https://github.com/dotnet/csharplang/blob/main/spec/types.md#array-types), such as `int[]`.
* [`Span<T>`](https://learn.microsoft.com/en-us/dotnet/api/system.span-1) and [`ReadOnlySpan<T>`](https://learn.microsoft.com/en-us/dotnet/api/system.readonlyspan-1).
* Types that support [collection initializers](https://github.com/dotnet/csharplang/blob/main/spec/expressions.md#collection-initializers), such as [`List<T>`](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1) and [`Dictionary<TKey, TValue>`](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2).

Further support is present for collection-like types not covered under the above, such as [`ImmutableArray<T>`](https://learn.microsoft.com/en-us/dotnet/api/system.collections.immutable.immutablearray-1), through a new API pattern that can be adopted directly on the type itself or through extension methods.

## Motivation
[motivation]: #motivation

* Collection-like values are hugely present in programming, algorithms, and especially in the C#/.NET ecosystem.  Nearly all programs will utilize these values to store data and send or receive data from other components. Currently, almost all C# programs must use many different and unfortunately verbose approaches to create instances of such values. Some approaches also have performance drawbacks. Here are some common examples:

    - Arrays, which require either `new Type[]` or `new[]` before the `{ ... }` values.

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dimohy · July 26, 2023, 12:02am

컬렉션 표현식 (구현됨, 17.7 P5에 반영)

드디어 컬렉션 표현식을 Visual Studio 2022 17.7 P5에서 테스트 해 볼 수 있습니다.

<PropertyGroup>
   <LangVersion>Preview</LangVersion>
</PropertyGroup>

이전에는 이렇게 써야 했다면

var oList = new int[] { 1, 2, 3, 4, 5 };

이제는 다음과 같이 사용할 수 있습니다.

int[] nList = [1, 2, 3, 4, 5];

스택에 배열을 생성하는 것도 다음처럼 사용할 수 있게 되었습니다.

Span<int> sList = [1, 2, 3, 4, 5];

패턴일치에도 사용할 수 있습니다.

var result = sList is [1, .., 5];

naratteu · July 26, 2023, 2:26am

제네릭별칭은 아직인가보군요