【C# 9.0 がやってきた】Build 2020 で .NET 5 Preview 4 公開

[ufcpp]

Microsoft Build に合わせていろいろとブログ公開が。

• Announcing .NET 5 Preview 4 and our journey to one .NET
• Releasing Today! Visual Studio 2019 v16.6 & v16.7 Preview
  • 16.6 Release Notes
  • 16.7 Preview 1 Release Notes
• Introducing .NET Multi-platform App UI
• Windows Forms Designer for .NET Core Released
• Announcing Entity Framework Core 5.0 Preview 4
• ML.NET Model Builder is now a part of Visual Studio
• Windows Terminal 1.0
• Windows Package Manager Preview
• Introducing WinUI 3 Preview 1
• The Windows Subsystem for Linux BUILD 2020 Summary
• DirectX is coming to the Windows Subsystem for Linux
• Expanding Visual Studio 2019 support for Visual Studio Codespaces
• Live Share, now with chat and audio support!

追記: C# チームも1日遅れでブログ出した

• Welcome to C# 9.0

正直、ブログ読みふけってて Build のキーノート(ブチザッキ参照)全然聞いてない。

1回の配信で触れる量じゃないし、とりあえずC# 9.0 の話を中心に(他はチャットの反応次第)。

C# 9.0:

• Language Feature Status
  • native int, target-typed new, pattern V3 の3つ、動作確認済み
  • pattern は「merged」になってないけど動いてる(変更の可能性ちょっとだけあり)
• Build の C# Today & Tomorrow デモ では Records と Top-level statements も動いてたけどこれは Build 用のブランチみたい
• 16.7.P1 milestone
• sharplab には Records ブランチと target-typed conditional ブランチ と Top-level statements ブランチあり

[ufcpp-live]

配信中に書き散らかした結果:

// new features in .NET 5 preview 4

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Runtime.InteropServices.ComTypes;
using System.Threading;

interface IA { int A(); }
interface IB : IA { int B(); }
interface IC : IA { int C(); }

class Ab : IB, IC
{
    public int A() => 2;
    public int B() => 3;
    public int C() => 5;
}

class Program
{
    static void Main()
    {
        Console.WriteLine(float.NaN == float.NaN); //false

        //// native int
        //nint i = 1;
        //nint u = 2;
        //Console.WriteLine(i + u);
    }

    // target-typed new
    static Dictionary<string, int> d = new()
    {
        { "a", 1 },
    };

    static void M1(object obj)
    {
        // !ReferenceEquals(obj, null)
        if (obj is { }) // 知ってないと意味不明
        {
        }
        // 同じ意味
        if (obj is not null) // 初見さんにやさしい
        {
        }

        // ユーザー定義の != があればそれを呼ぶ
        if (obj != null)
        {
        }

        IA a = obj is null
            ? (IA)null
            : (IB)null;

        int b1 = obj is null
            ? (byte)1
            : (int)2;

        int? c1 = obj is null
            ? (int?)null
            : (int)2;

        IA aa = obj switch
        {
            IB b => b,
            IC c => c,
        };

        M((short)1, obj is null ? (int)1 : (short)2);
    }

    static void M(short x, short y) { }
    static void M(int x, int y) { }

    static void M<T>(T obj)
        where T : IB, IC // and
    {
        obj.A();
        obj.B();
        obj.C();
    }

    //static void M<T>(T obj)
    //    where T : IB or IC // 要望はあり。別提案
    //{
    //    obj.A();
    //    obj.B();
    //    obj.C();
    //}

    static int M11(object obj) => obj switch
    {
        byte => 1,
        sbyte => 1,
        ushort => 2,
        short => 2,
        int => 4,
        uint => 4,
        long => 8,
        ulong => 8,
        DateTime => 8,
        DateTimeOffset => 16,
        Guid => 16,
        _ => -1,
    };

    static int M11(bool b) => b switch
    {
        true => 1,
        false => 0,
    };

    class A { }
    class B : A { }
    class C : A { }

#nullable enable
    // pattern V3 (and, or, not, simple type, parenthesized...)
    static int M(object? obj) => obj switch
    {
        IB b and IC c => b.A() * b.B() * c.C(),
        (IA or IB) and var a => a.A(),
        //(B or C) and var a => a.A(), // object です(今のところ)。A にする提案あり
        string s => s.Length,
        //{ } a => a.GetHashCode(), // not null の意味含む(初見に厳しい)
        not null and var a => a.GetHashCode(),
    };

    // pattern V3 (rerational, exhaustivity check)
    static int M(float value) => value switch
    {
        < (10 * 10) => 1,
        >= 100 and < 500 => 2,
        5 * 100 => 5,
        > 500 => 3,
        float.NaN => 4,
        //_ => 2,
    };

    static int M111(float value) => value switch
    {
        var x when x < 100 => 1,
        var x when x >= 100 && x <= 500 => 2,
        var x when x > 500 => 3,
    };

    // pattern V3 (byte exhaustivity check)
    static int M(byte ascii) => ascii switch
    {
        <= 31 => 0, // control
        32 => 2, // white space
        <= 47 => 3, // symbol
        <= 57 => 4, // number
        <= 64 => 3, // symbol
        >= (int)'A' and <= (int)'Z' => 5, // letter A-Z
        >= (int)'a' and <= (int)'z' => 5, // letter a-z
        > (int)'z' and <= 126 => 3,
        127 => 0,
        >= 128 => 6, // non-asci
    };
}

[ufcpp-live]

https://youtu.be/fZxRZgWYqq0