mcs/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 #if NET_2_0
  34
  35 using System.Reflection;
  36 using System.Collections.Generic;
  37 using System.Runtime.CompilerServices;
  38 using System.Runtime.InteropServices;
  39
  40 namespace System
  41 {
  42         [ComVisible (true)]
  43         public static class Nullable {
  44
  45 #if NET_2_1
  46                 [ComVisible (false)]
  47 #endif
  48                 public static int Compare<T> (T? value1, T? value2) where T: struct
  49                 {
  50                         if (value1.has_value) {
  51                                 if (!value2.has_value)
  52                                         return 1;
  53
  54                                 return Comparer<T>.Default.Compare (value1.value, value2.value);
  55                         }
  56
  57                         return value2.has_value ? -1 : 0;
  58                 }
  59
  60 #if NET_2_1
  61                 [ComVisible (false)]
  62 #endif
  63                 public static bool Equals<T> (T? value1, T? value2) where T: struct
  64                 {
  65                         if (value1.has_value != value2.has_value)
  66                                 return false;
  67
  68                         if (!value1.has_value)
  69                                 return true;
  70
  71                         return EqualityComparer<T>.Default.Equals (value1.value, value2.value);
  72                 }
  73
  74                 public static Type GetUnderlyingType (Type nullableType)
  75                 {
  76                         if (nullableType == null)
  77                                 throw new ArgumentNullException ("nullableType");
  78                         if (nullableType.IsGenericType && nullableType.GetGenericTypeDefinition () == typeof (Nullable<>))
  79                                 return nullableType.GetGenericArguments ()[0];
  80                         else
  81                                 return null;
  82                 }
  83         }
  84
  85         [Serializable]
  86         public struct Nullable<T> where T: struct
  87         {
  88                 #region Sync with runtime code
  89                 internal T value;
  90                 internal bool has_value;
  91                 #endregion
  92
  93                 public Nullable (T value)
  94                 {
  95                         this.has_value = true;
  96                         this.value = value;
  97                 }
  98
  99                 public bool HasValue {
 100                         get { return has_value; }
 101                 }
 102
 103                 public T Value {
 104                         get {
 105                                 if (!has_value)
 106                                         throw new InvalidOperationException ("Nullable object must have a value.");
 107
 108                                 return value;
 109                         }
 110                 }
 111
 112                 public override bool Equals (object other)
 113                 {
 114                         if (other == null)
 115                                 return has_value == false;
 116                         if (!(other is Nullable<T>))
 117                                 return false;
 118
 119                         return Equals ((Nullable <T>) other);
 120                 }
 121
 122                 bool Equals (Nullable<T> other)
 123                 {
 124                         if (other.has_value != has_value)
 125                                 return false;
 126
 127                         if (has_value == false)
 128                                 return true;
 129
 130                         return other.value.Equals (value);
 131                 }
 132
 133                 public override int GetHashCode ()
 134                 {
 135                         if (!has_value)
 136                                 return 0;
 137
 138                         return value.GetHashCode ();
 139                 }
 140
 141                 public T GetValueOrDefault ()
 142                 {
 143                         return GetValueOrDefault (default (T));
 144                 }
 145
 146                 public T GetValueOrDefault (T defaultValue)
 147                 {
 148                         if (!has_value)
 149                                 return defaultValue;
 150                         else
 151                                 return value;
 152                 }
 153
 154                 public override string ToString ()
 155                 {
 156                         if (has_value)
 157                                 return value.ToString ();
 158                         else
 159                                 return String.Empty;
 160                 }
 161
 162                 public static implicit operator Nullable<T> (T value)
 163                 {
 164                         return new Nullable<T> (value);
 165                 }
 166
 167                 public static explicit operator T (Nullable<T> value)
 168                 {
 169                         return value.Value;
 170                 }
 171
 172                 //
 173                 // These are called by the JIT
 174                 //
 175
 176                 //
 177                 // JIT implementation of box valuetype System.Nullable`1<T>
 178                 //
 179                 static object Box (T? o)
 180                 {
 181                         if (!o.has_value)
 182                                 return null;
 183
 184                         return o.value;
 185                 }
 186
 187                 static T? Unbox (object o)
 188                 {
 189                         if (o == null)
 190                                 return null;
 191                         return (T) o;
 192                 }
 193         }
 194 }
 195 #endif