class/corlib/System/Nullable.cs

   1 //
   2 // System.Nullable.cs
   3 //
   4 // Martin Baulig (martin@ximian.com)
   5 // Marek Safar   (marek.safar@gmail.com)
   6 //
   7 // (C) 2004 Novell, Inc.
   8 //
   9
  10 //
  11 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
  12 //
  13 // Permission is hereby granted, free of charge, to any person obtaining
  14 // a copy of this software and associated documentation files (the
  15 // "Software"), to deal in the Software without restriction, including
  16 // without limitation the rights to use, copy, modify, merge, publish,
  17 // distribute, sublicense, and/or sell copies of the Software, and to
  18 // permit persons to whom the Software is furnished to do so, subject to
  19 // the following conditions:
  20 //
  21 // The above copyright notice and this permission notice shall be
  22 // included in all copies or substantial portions of the Software.
  23 //
  24 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  25 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  26 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  27 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  28 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  29 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  30 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  31 //
  32
  33 using System.Reflection;
  34 using System.Collections.Generic;
  35 using System.Runtime.CompilerServices;
  36 using System.Runtime.InteropServices;
  37
  38 namespace System
  39 {
  40         [ComVisible (true)]
  41         public static class Nullable {
  42
  43 #if NET_2_1
  44                 [ComVisible (false)]
  45 #endif
  46                 public static int Compare<T> (T? value1, T? value2) where T: struct
  47                 {
  48                         if (value1.has_value) {
  49                                 if (!value2.has_value)
  50                                         return 1;
  51
  52                                 return Comparer<T>.Default.Compare (value1.value, value2.value);
  53                         }
  54
  55                         return value2.has_value ? -1 : 0;
  56                 }
  57
  58 #if NET_2_1
  59                 [ComVisible (false)]
  60 #endif
  61                 public static bool Equals<T> (T? value1, T? value2) where T: struct
  62                 {
  63                         if (value1.has_value != value2.has_value)
  64                                 return false;
  65
  66                         if (!value1.has_value)
  67                                 return true;
  68
  69                         return EqualityComparer<T>.Default.Equals (value1.value, value2.value);
  70                 }
  71
  72                 public static Type GetUnderlyingType (Type nullableType)
  73                 {
  74                         if (nullableType == null)
  75                                 throw new ArgumentNullException ("nullableType");
  76                         if (nullableType.IsGenericType && nullableType.GetGenericTypeDefinition () == typeof (Nullable<>))
  77                                 return nullableType.GetGenericArguments ()[0];
  78                         else
  79                                 return null;
  80                 }
  81         }
  82
  83         [Serializable]
  84         public struct Nullable<T> where T: struct
  85         {
  86                 #region Sync with runtime code
  87                 internal T value;
  88                 internal bool has_value;
  89                 #endregion
  90
  91                 public Nullable (T value)
  92                 {
  93                         this.has_value = true;
  94                         this.value = value;
  95                 }
  96
  97                 public bool HasValue {
  98                         get { return has_value; }
  99                 }
 100
 101                 public T Value {
 102                         get {
 103                                 if (!has_value)
 104                                         throw new InvalidOperationException ("Nullable object must have a value.");
 105
 106                                 return value;
 107                         }
 108                 }
 109
 110                 public override bool Equals (object other)
 111                 {
 112                         if (other == null)
 113                                 return has_value == false;
 114                         if (!(other is Nullable<T>))
 115                                 return false;
 116
 117                         return Equals ((Nullable <T>) other);
 118                 }
 119
 120                 bool Equals (Nullable<T> other)
 121                 {
 122                         if (other.has_value != has_value)
 123                                 return false;
 124
 125                         if (has_value == false)
 126                                 return true;
 127
 128                         return other.value.Equals (value);
 129                 }
 130
 131                 public override int GetHashCode ()
 132                 {
 133                         if (!has_value)
 134                                 return 0;
 135
 136                         return value.GetHashCode ();
 137                 }
 138
 139                 public T GetValueOrDefault ()
 140                 {
 141                         return has_value ? value : default (T);
 142                 }
 143
 144                 public T GetValueOrDefault (T defaultValue)
 145                 {
 146                         return has_value ? value : defaultValue;
 147                 }
 148
 149                 public override string ToString ()
 150                 {
 151                         if (has_value)
 152                                 return value.ToString ();
 153                         else
 154                                 return String.Empty;
 155                 }
 156
 157                 public static implicit operator Nullable<T> (T value)
 158                 {
 159                         return new Nullable<T> (value);
 160                 }
 161
 162                 public static explicit operator T (Nullable<T> value)
 163                 {
 164                         return value.Value;
 165                 }
 166
 167                 //
 168                 // These are called by the JIT
 169                 //
 170 #pragma warning disable 169
 171                 //
 172                 // JIT implementation of box valuetype System.Nullable`1<T>
 173                 //
 174                 static object Box (T? o)
 175                 {
 176                         if (!o.has_value)
 177                                 return null;
 178
 179                         return o.value;
 180                 }
 181
 182                 static T? Unbox (object o)
 183                 {
 184                         if (o == null)
 185                                 return null;
 186                         return (T) o;
 187                 }
 188 #pragma warning restore 169
 189         }
 190 }