c# 8系列(一)

readonly struct members

void Main()
{
    // See https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8
}

public struct Point
{
    public double X { get; set; }
    public double Y { get; set; }   
    
    // Note the readonly modifier. This will generate a compiler error if you try and modify
    // the struct's fields within the method.   
    public readonly override string ToString() => $"({X}, {Y}) is {Distance} from the origin";

    // We need a readonly modifier here to avoid a warning in the method above.
    public readonly double Distance => Math.Sqrt (X * X + Y * Y);
}

default interface members

void Main()
{
    ILogger foo = new Logger();
    foo.Log (new Exception ("test"));   
}

class Logger : ILogger
{   
    public void Log (string message) => Console.WriteLine (message);
}

interface ILogger
{
    void Log (string message);  
    
    // Adding a new member to an interface need not break implementors:
    public void Log (Exception ex) => Log (ExceptionHeader + ex.Message);
    
    // The static modifier (and other modifiers) are now allowed:
    static string ExceptionHeader = "Exception: ";
}

switch expressions

void Main()
{
    var color = FromRainbow (Rainbow.Green);
    new Panel { BackColor = color }.Dump();
}

public static Color FromRainbow (Rainbow colorBand) =>
    colorBand switch
    {
        Rainbow.Red => Color.Red,
        Rainbow.Orange => Color.Orange,
        Rainbow.Yellow => Color.Yellow,
        Rainbow.Green => Color.Green,
        Rainbow.Blue => Color.Blue,
        Rainbow.Indigo => Color.Indigo,
        Rainbow.Violet => Color.Violet,
        _ => throw new ArgumentException (message: "invalid enum value", paramName: nameof (colorBand)),
    };
    
public enum Rainbow
{
    Red,
    Orange,
    Yellow,
    Green,
    Blue,
    Indigo,
    Violet
}

property patterns

void Main()
{
    var address = new Address { State = "WA" };
    ComputeSalesTax (address, 100).Dump();
}

static decimal ComputeSalesTax (Address location, decimal salePrice) =>
    location switch
    {
        { State: "WA" } => salePrice * 0.06M,
        { State: "MN" } => salePrice * 0.75M,
        { State: "MI" } => salePrice * 0.05M,
        // other cases removed for brevity...
        _ => 0M
    };
    
class Address
{
    public string State;
}

本文作者：wwmin
微信公众号: DotNet技术说
本文链接：https://www.jianshu.com/p/ce545c355555
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