浅析C# 9.0 新特性之 Lambda 弃元参数

var tuple = (1, 2, 3, 4, 5);
(_, _, _, _, var fifth) = tuple;

var obj = CultureInfo.CurrentCulture.DateTimeFormat;

switch (obj)
{
  case IFormatProvider fmt:
    Console.WriteLine($"{fmt} object");
    break;
  case null:
    Console.Write("A null object reference");
    break;
  case object _:
    Console.WriteLine("Some object type without format information");
    break;
}

if (obj is object _)
{
  ...
}

var point = new Point(10, 10);
// 只要 x, 不关心 y
point.GetCoordinates(out int x, out _);

void Test(Dto dto)
{
  _ = dto ?? throw new ArgumentNullException(nameof(dto));
}

// C# 9 之前
Func<int, int, int> zero = (a, b) => 0;
Func<int, int, int> func = delegate (int a, int b) { return 0; };

// C# 9
Func<int, int, int> zero = (_, _) => 0;
Func<int, int, int> func = delegate (int _, int _) { return 0; };