mcs/class/corlib/System/Nullable.cs

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