C# Next (C# 12 후보) - slog

dimohy · 3월 18, 2023, 11:36오후

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 · 3월 18, 2023, 11:50오후

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 · 3월 19, 2023, 12:08오전

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 · 3월 19, 2023, 12:11오전

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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