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主に C#, .NET, Azure の備忘録です。たまに日記。

.NET Core 3 Previewの気になることまとめ

.NET Core C#

※ 2019/08/17 15:16 更新 Preview5からPreview7を追記

.NET Core 3 Previewについて公式ブログにある内容から、個人的に気になるものをまとめます。完全に備忘録。
なお .NET Core 3 Previewはこれまで4回7回リリースされています。

devblogs.microsoft.com

Preview1

Resources

Overview

WPF csproj

<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>netcoreapp3.0</TargetFramework>
    <UseWPF>true</UseWPF>
  </PropertyGroup>
</Project>

<UseWPF>true</UseWPF>

WinForms csproj

<ProjectSdk="Microsoft.NET.Sdk.WindowsDesktop">
  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>netcoreapp3.0</TargetFramework>
    <UseWindowsForms>true</UseWindowsForms>
  </PropertyGroup>
</Project>

<UseWindowsForms>true</UseWindowsForms>

System.Text.Json.Utf8JsonReader

public static void Utf8JsonReaderLoop(ReadOnlySpan<byte> dataUtf8)
{
    var json = new Utf8JsonReader(dataUtf8, isFinalBlock: true, state: default);

    while (json.Read())
    {
        JsonTokenType tokenType = json.TokenType;
        ReadOnlySpan<byte> valueSpan = json.ValueSpan;
        switch (tokenType)
        {
            case JsonTokenType.StartObject:
            case JsonTokenType.EndObject:
                break;
            case JsonTokenType.StartArray:
            case JsonTokenType.EndArray:
                break;
            case JsonTokenType.PropertyName:
                break;
            case JsonTokenType.String:
                string valueString = json.GetStringValue();
                break;
            case JsonTokenType.Number:
                if (!json.TryGetInt32Value(out int valueInteger))
                {
                    throw new FormatException();
                }
                break;
            case JsonTokenType.True:
            case JsonTokenType.False:
                bool valueBool = json.GetBooleanValue();
                break;
            case JsonTokenType.Null:
                break;
            default:
                throw new ArgumentException();
        }
    }

    dataUtf8 = dataUtf8.Slice((int)json.BytesConsumed);
    JsonReaderState state = json.CurrentState;
}

IAsyncEnumerable<T>

async IAsyncEnumerable<int> GetBigResultsAsync()
{
    await foreach (var result in GetResultsAsync())
    {
        if (result > 20) yield return result; 
    }
}

Interfaceのメソッドの既定の実装

interface ILogger
{
    void Log(LogLevel level, string message);
    void Log(Exception ex) => Log(LogLevel.Error, ex.ToString()); // New overload
}
class ConsoleLogger : ILogger
{
    public void Log(LogLevel level, string message) { ... }
    // Log(Exception) gets default implementation
}

MetadataLoadContext

var paths = new string[] {@"C:\myapp\mscorlib.dll", @"C:\myapp\myapp.dll"};
var resolver = new PathAssemblyResolver(paths);
using (var lc = new MetadataLoadContext(resolver))
{
    Assembly a = lc.LoadFromAssemblyName("myapp");
    Type myInterface = a.GetType("MyApp.IPluginInterface");
    foreach (Type t in a.GetTypes())
    {
        if (t.IsClass && myInterface.IsAssignableFrom(t))
            Console.WriteLine($"Class {t.FullName} implements IPluginInterface");
    }
}

Preview2

Resources

Overview

Switch式

単一の項目
static string Display(object o) => o switch
{
    Point { X: 0, Y: 0 }         => "origin",
    Point { X: var x, Y: var y } => $"({x}, {y})",
    _                            => "unknown"
};
複数の項目
static State ChangeState(State current, Transition transition, bool hasKey) =>
    (current, transition) switch
    {
        (Opened, Close)              => Closed,
        (Closed, Open)               => Opened,
        (Closed, Lock)   when hasKey => Locked,
        (Locked, Unlock) when hasKey => Closed,
        _ => throw new InvalidOperationException($"Invalid transition")
};

System.Text.Json.Utf8JsonWriter

static int WriteJson(IBufferWriter<byte> output, long[] extraData)
{
    var json = new Utf8JsonWriter(output, state: default);

    json.WriteStartObject();

    json.WriteNumber("age", 15, escape: false);
    json.WriteString("date", DateTime.Now);
    json.WriteString("first", "John");
    json.WriteString("last", "Smith");

    json.WriteStartArray("phoneNumbers", escape: false);
    json.WriteStringValue("425-000-1212", escape: false);
    json.WriteStringValue("425-000-1213");
    json.WriteEndArray();

    json.WriteStartObject("address");
    json.WriteString("street", "1 Microsoft Way");
    json.WriteString("city", "Redmond");
    json.WriteNumber("zip", 98052);
    json.WriteEndObject();

    json.WriteStartArray("ExtraArray");
    for (var i = 0; i < extraData.Length; i++)
    {
        json.WriteNumberValue(extraData[i]);
    }
    json.WriteEndArray();

    json.WriteEndObject();

    json.Flush(isFinalBlock: true);

    return (int)json.BytesWritten;
}

System.Text.Json.JsonDocument

static double ParseJson()
{
    const string json = " [ { \"name\": \"John\" }, [ \"425-000-1212\", 15 ], { \"grades\": [ 90, 80, 100, 75 ] } ]";

    double average = -1;

    using (JsonDocument doc = JsonDocument.Parse(json))
    {
        JsonElement root = doc.RootElement;
        JsonElement info = root[1];

        string phoneNumber = info[0].GetString();
        int age = info[1].GetInt32();

        JsonElement grades = root[2].GetProperty("grades");

        double sum = 0;
        foreach (JsonElement grade in grades.EnumerateArray())
        {
            sum += grade.GetInt32();
        }

        int numberOfCourses = grades.GetArrayLength();
        average = sum / numberOfCourses;
    }

    return average;
}

Preview3

Resources

Overview

Index and Range

// start with int[]
int[] nums = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int lastNum = nums[^1]; // 10
int[] subsetNums = nums[2..6]; // {3, 4, 5, 6}
 
// Create a Memory<int> using arrayofNums as input
// Create no-copy slices of the array
Memory<int> numbers = nums;
Memory<int> lastTwoNums = numbers.Slice(^2); // {9, 10}
Memory<int> middleNums = numbers.Slice(4..8); // {5, 6, 7, 8}
 
// Create a substring using a range
string myString = "0123456789ABCDEF";
string substring = myString[0..5]; // "01234"
 
// Create a Memory<char> using a range
ReadOnlyMemory<char> myChars = myString.AsMemory();
ReadOnlyMemory<char> firstChars = myChars[0..5]; // {'0', '1', '2', '3', '4'}
 
// Get an offset with an Index
Index indexFromEnd = Index.FromEnd(3); // equivalent to [^3]
int offsetFromLength = indexFromEnd.GetOffset(10); // 7
int value = nums[offsetFromLength]; // 8
 
// Get an offset with a Range
Range rangeFromEnd = 5..^0;
(int offset, int length) = rangeFromEnd.GetOffsetAndLength(10); // offset = 5, length = 5
Memory<int> values = numbers.Slice(offset, length); // {6, 7, 8, 9, 10}

.NET Standard 2.1

<Project Sdk="Microsoft.NET.Sdk">
 
  <PropertyGroup>
    <TargetFramework>netstandard2.1</TargetFramework>
  </PropertyGroup>
 
</Project>

AssemblyDependencyResolver

var resolver = new AssemblyDependencyResolver(pluginPath);
var assemblyPath = resolver.ResolveAssemblyToPath(assemblyName);

Preview4

Resources

Overview

Preview5

Resources

Overview

Preview6

Resources

Overview

ReadyToRun

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.0</TargetFramework>
    <PublishReadyToRun>true</PublishReadyToRun>
  </PropertyGroup>

</Project>

Preview7

Resources

Overview

  • Go Live
    • 運用環境で使えるレベルになったということ。ただし実際に運用環境で使用する前には十分なテストが必要。
  • .NET Core SDKのサイズが改善