C#可空类型详解 C#基础语法：可空类型详解

[Serializable, StructLayout(LayoutKind.Sequential)]
public struct Nullable<T> where T :struct
{
 private Boolean hasValue= false;
 internal T value= default(T);

public Nullable(T value)
 {
this.value= value;
this.hasValue= true;
 }

public Boolean HasValue {get {return hasValue; } }

public T Value
 {
get
  {
  if (!hasValue)
    {
   throw new InvalidOperationException("Nullable object must have a value.");
    }
   return value;
  }
 }

public T GetValueOrDefault() {return value; }
public T GetValueOrDefault(T defaultValue)
 {
if(!HasValue)return defaultValue;
return value;
 }

public override Boolean Equals(object other)
 {
if(!HasValue)return (other== null);
if(other== null)return false;
return value.Equals(other);
 }

public override int GetHashCode()
 {
if(!HasValue)return 0;
return value.GetHashCode();
 }

public override string ToString()
 {
if(!HasValue)return "";
return value.ToString();
 }

public static implicit operator Nullable<T>(T value)
 {
return new Nullable<T>(value);
 }
}

Console.WriteLine("========可空类型操作演示========\n");
      Console.WriteLine("\n=========Nullable<T>===========\n");
      Nullable<int> x = 5;
      Nullable<bool> y = false;
      Nullable<double> z = 5.20;
      Nullable<char> n = null;
      Console.WriteLine("x.HasValue={0},   x.Value={1}",x.HasValue,x.Value);
      Console.WriteLine("y.HasValue={0},   y.Value={1}", y.HasValue, y.Value);
      Console.WriteLine("z.HasValue={0},   z.Value={1}", z.HasValue, z.Value);
      Console.WriteLine("n.HasValue={0},   n.Value={1}",n.HasValue, n.GetValueOrDefault());
      Console.WriteLine("\n============== T? ============\n");
      int? X = 5;
      bool? Y = false;
      double? Z = 5.20;
      char? N = null;
      int?[] arr ={1,2,3,4,5};//一个可空类型的数组
      Console.WriteLine("X.HasValue={0},   X.Value={1}", X.HasValue,X.Value);
      Console.WriteLine("y.HasValue={0},   Y.Value={1}", Y.HasValue, Y.Value);
      Console.WriteLine("Z.HasValue={0},   Z.Value={1}", Z.HasValue, Z.Value);
      Console.WriteLine("N.HasValue={0},   N.Value={1}", N.HasValue, N.GetValueOrDefault());
      Console.WriteLine("\n================================\n");
      Console.ReadKey();