mcs/class/corlib/System/Nullable.cs

   1 //
   2 // System.Nullable
   3 //
   4 // Martin Baulig (martin@ximian.com)
   5 //
   6 // (C) 2004 Novell, Inc.
   7 //
   8
   9 //
  10 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
  11 //
  12 // Permission is hereby granted, free of charge, to any person obtaining
  13 // a copy of this software and associated documentation files (the
  14 // "Software"), to deal in the Software without restriction, including
  15 // without limitation the rights to use, copy, modify, merge, publish,
  16 // distribute, sublicense, and/or sell copies of the Software, and to
  17 // permit persons to whom the Software is furnished to do so, subject to
  18 // the following conditions:
  19 //
  20 // The above copyright notice and this permission notice shall be
  21 // included in all copies or substantial portions of the Software.
  22 //
  23 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  24 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  25 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  26 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  27 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  28 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  29 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  30 //
  31
  32 using System.Reflection;
  33 #if NET_2_0
  34 using System.Collections.Generic;
  35 #endif
  36 using System.Runtime.CompilerServices;
  37
  38 #if NET_2_0
  39 namespace System {
  40         public static class Nullable {
  41                 public static int Compare<T> (Nullable<T> left, Nullable<T> right) where T: struct
  42                 {
  43                         IComparable icomparable = left.value as IComparable;
  44                         if (icomparable == null)
  45                                 throw new ArgumentException ("At least one object must implement IComparable.");
  46                         if (left.has_value == false && right.has_value == false)
  47                                 return 0;
  48                         if (!left.has_value)
  49                                 return -1;
  50                         if (!right.has_value)
  51                                 return 1;
  52
  53                         return icomparable.CompareTo (right.value);
  54                 }
  55
  56                 public static bool Equals<T> (Nullable <T> value1, Nullable<T> value2) where T: struct
  57                 {
  58                         return value1.Equals (value2);
  59                 }
  60
  61                 public static Type GetUnderlyingType (Type nullableType)
  62                 {
  63                         if (nullableType == null)
  64                                 throw new ArgumentNullException ("nullableType");
  65                         if (nullableType.IsGenericType && nullableType.GetGenericTypeDefinition () == typeof (Nullable<>))
  66                                 return nullableType.GetGenericArguments ()[0];
  67                         else
  68                                 return null;
  69                 }
  70         }
  71
  72         [Serializable]
  73         public struct Nullable<T> where T: struct
  74         {
  75                 #region Sync with runtime code
  76                 internal T value;
  77                 internal bool has_value;
  78                 #endregion
  79
  80                 public Nullable (T value)
  81                 {
  82                         this.has_value = true;
  83                         this.value = value;
  84                 }
  85
  86                 public bool HasValue {
  87                         get { return has_value; }
  88                 }
  89
  90                 public T Value {
  91                         get {
  92                                 if (!has_value)
  93                                         throw new InvalidOperationException ("Nullable object must have a value.");
  94
  95                                 return value;
  96                         }
  97                 }
  98
  99                 public override bool Equals (object other)
 100                 {
 101                         if (other == null)
 102                                 return has_value == false;
 103                         if (!(other is Nullable<T>))
 104                                 return false;
 105
 106                         return Equals ((Nullable <T>) other);
 107                 }
 108
 109                 bool Equals (Nullable<T> other)
 110                 {
 111                         Nullable<T> no = (Nullable<T>) other;
 112                         if (no.has_value != has_value)
 113                                 return false;
 114
 115                         if (has_value == false)
 116                                 return true;
 117
 118                         return no.value.Equals (value);
 119                 }
 120
 121                 public override int GetHashCode ()
 122                 {
 123                         if (!has_value)
 124                                 return 0;
 125
 126                         return value.GetHashCode ();
 127                 }
 128
 129                 public T GetValueOrDefault ()
 130                 {
 131                         return GetValueOrDefault (default (T));
 132                 }
 133
 134                 public T GetValueOrDefault (T def_value)
 135                 {
 136                         if (!has_value)
 137                                 return def_value;
 138                         else
 139                                 return value;
 140                 }
 141
 142                 public override string ToString ()
 143                 {
 144                         if (has_value)
 145                                 return value.ToString ();
 146                         else
 147                                 return String.Empty;
 148                 }
 149
 150                 public static implicit operator Nullable<T> (T value)
 151                 {
 152                         return new Nullable<T> (value);
 153                 }
 154
 155                 public static explicit operator T (Nullable<T> value)
 156                 {
 157                         return value.Value;
 158                 }
 159
 160                 // These are called by the JIT
 161                 // Ironicly, the C#  code is the same for these two,
 162                 // however, on the inside they do somewhat different things
 163                 static object Box (T? o)
 164                 {
 165                         if (o == null)
 166                                 return null;
 167                         return (T) o;
 168                 }
 169
 170                 static T? Unbox (object o)
 171                 {
 172                         if (o == null)
 173                                 return null;
 174                         return (T) o;
 175                 }
 176         }
 177 }
 178 #endif