C#8.0 部分语法特性

Null 合并赋值

List<int> numbers = null;
int? i = null;

numbers ??= new List<int>();
numbers.Add(i ??= 17); //i null 赋值为17
numbers.Add(i ??= 20); //i 为17 值不改变

Console.WriteLine(string.Join(" ", numbers));  // output: 17 17
Console.WriteLine(i);  // output: 17

索引和范围

  string a1 = "123456";
  string s = a1[..];      //123456
  string s1 = a1[..3];    //123
  string s2 = a1[3..];    //456
  string s3 = a1[2..4];   //34