my_note

- 日理万妓 2023-10-09 11:56 52阅读 0赞

1.C# $ 内插字符串  Console.WriteLine($"The value of pi is {Math.PI}");  替代string.format
    
     
    
    2. switch  的新写法 colorBand 是枚举
    
    public static RGBColor FromRainbow(Rainbow colorBand) =>
    colorBand switch
    {
    Rainbow.Red => new RGBColor(0xFF, 0x00, 0x00),
    Rainbow.Orange => new RGBColor(0xFF, 0x7F, 0x00),
    Rainbow.Yellow => new RGBColor(0xFF, 0xFF, 0x00),
    Rainbow.Green => new RGBColor(0x00, 0xFF, 0x00),
    Rainbow.Blue => new RGBColor(0x00, 0x00, 0xFF),
    Rainbow.Indigo => new RGBColor(0x4B, 0x00, 0x82),
    Rainbow.Violet => new RGBColor(0x94, 0x00, 0xD3),
    _ => throw new ArgumentException(message: "invalid enum value", paramName: nameof(colorBand)),
    };
    
     
    
    public 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
    }; //属性模式
    
     
    
    
    List<modelTest> list = new List<modelTest>();
    list.Add(new modelTest {id=1, name="aaa", address="aaaaaa" });
    list.Add(new modelTest { id = 2, name = "bbb", address = "bbbbbb" });
    list.Add(new modelTest { id = 3, name = "ccc", address = "cccccc" });
    list.Add(new modelTest { id = 4, name = "ddd", address = "dddddd" });
    list.Add(new modelTest { id = 5, name = "eee", address = "eeeeee" });
    
    var aa= list.Where(x=>x.name== "aaa").ToList(); 
    var bb = list.Where(x => x.name == "bbbb");
    var dd = list.Where(x => x.name == "bbbb").ToList();不会报错 不为null  但是count为0
    var eecc = list.Where(x => x.name == "bbbb").First(); 序列为空 报错
    var eecctt = list.Where(x => x.name == "bbbb").ToList().First(); 序列为空 报错
    var dddddd = list.Where(x => x.name == "bbbb").FirstOrDefault(); 不会报错 为空 返回null
    var ccc= "";

转载于:https://www.cnblogs.com/muxueyuan/p/11338520.html

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