mcs/mcs/const.cs

   1 //
   2 // const.cs: Constant declarations.
   3 //
   4 // Author:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Marek Safar (marek.safar@seznam.cz)
   7 //
   8 // (C) 2001 Ximian, Inc.
   9 //
  10 //
  11
  12 namespace Mono.CSharp {
  13
  14         using System;
  15         using System.Reflection;
  16         using System.Reflection.Emit;
  17         using System.Collections;
  18
  19         public interface IConstant
  20         {
  21                 void CheckObsoleteness (Location loc);
  22                 bool ResolveValue ();
  23                 Constant Value { get; }
  24         }
  25
  26         public class Const : FieldMember, IConstant {
  27                 Constant value;
  28                 bool in_transit;
  29                 bool define_called;
  30
  31                 public const int AllowedModifiers =
  32                         Modifiers.NEW |
  33                         Modifiers.PUBLIC |
  34                         Modifiers.PROTECTED |
  35                         Modifiers.INTERNAL |
  36                         Modifiers.PRIVATE;
  37
  38                 public Const (DeclSpace parent, Expression constant_type, string name,
  39                               Expression expr, int mod_flags, Attributes attrs, Location loc)
  40                         : base (parent, constant_type, mod_flags, AllowedModifiers,
  41                                 new MemberName (name, loc), attrs)
  42                 {
  43                         initializer = expr;
  44                         ModFlags |= Modifiers.STATIC;
  45                 }
  46
  47                 protected override bool CheckBase ()
  48                 {
  49                         // Constant.Define can be called when the parent type hasn't yet been populated
  50                         // and it's base types need not have been populated.  So, we defer this check
  51                         // to the second time Define () is called on this member.
  52                         if (Parent.PartialContainer.BaseCache == null)
  53                                 return true;
  54                         return base.CheckBase ();
  55                 }
  56
  57                 /// <summary>
  58                 ///   Defines the constant in the @parent
  59                 /// </summary>
  60                 public override bool Define ()
  61                 {
  62                         // Because constant define can be called from other class
  63                         if (define_called) {
  64                                 CheckBase ();
  65                                 return FieldBuilder != null;
  66                         }
  67
  68                         define_called = true;
  69
  70                         if (!base.Define ())
  71                                 return false;
  72
  73                         Type ttype = MemberType;
  74                         if (!IsConstantTypeValid (ttype)) {
  75                                 Error_InvalidConstantType (ttype, Location);
  76                                 return false;
  77                         }
  78
  79                         while (ttype.IsArray)
  80                             ttype = TypeManager.GetElementType (ttype);
  81
  82                         FieldAttributes field_attr = FieldAttributes.Static | Modifiers.FieldAttr (ModFlags);
  83                         // Decimals cannot be emitted into the constant blob.  So, convert to 'readonly'.
  84                         if (ttype == TypeManager.decimal_type) {
  85                                 field_attr |= FieldAttributes.InitOnly;
  86                                 Parent.PartialContainer.RegisterFieldForInitialization (this);
  87                         } else {
  88                                 field_attr |= FieldAttributes.Literal;
  89                         }
  90
  91                         FieldBuilder = Parent.TypeBuilder.DefineField (Name, MemberType, field_attr);
  92
  93                         TypeManager.RegisterConstant (FieldBuilder, this);
  94
  95                         return true;
  96                 }
  97
  98                 public static bool IsConstantTypeValid (Type t)
  99                 {
 100                         if (TypeManager.IsBuiltinOrEnum (t))
 101                                 return true;
 102
 103                         if (t.IsPointer || t.IsValueType)
 104                                 return false;
 105
 106                         if (TypeManager.IsGenericParameter (t))
 107                                 return false;
 108
 109                         return true;
 110                 }
 111
 112                 /// <summary>
 113                 ///  Emits the field value by evaluating the expression
 114                 /// </summary>
 115                 public override void Emit ()
 116                 {
 117                         if (!ResolveValue ())
 118                                 return;
 119
 120                         if (value.Type == TypeManager.decimal_type) {
 121                                 Decimal d = ((DecimalConstant)value).Value;
 122                                 int[] bits = Decimal.GetBits (d);
 123                                 object[] args = new object[] { (byte)(bits [3] >> 16), (byte)(bits [3] >> 31), (uint)bits [2], (uint)bits [1], (uint)bits [0] };
 124                                 CustomAttributeBuilder cab = new CustomAttributeBuilder (TypeManager.decimal_constant_attribute_ctor, args);
 125                                 FieldBuilder.SetCustomAttribute (cab);
 126                         }
 127                         else{
 128                                 FieldBuilder.SetConstant (value.GetTypedValue ());
 129                         }
 130
 131                         base.Emit ();
 132                 }
 133
 134                 public static void Error_ExpressionMustBeConstant (Location loc, string e_name)
 135                 {
 136                         Report.Error (133, loc, "The expression being assigned to `{0}' must be constant", e_name);
 137                 }
 138
 139                 public static void Error_CyclicDeclaration (MemberCore mc)
 140                 {
 141                         Report.Error (110, mc.Location, "The evaluation of the constant value for `{0}' involves a circular definition",
 142                                 mc.GetSignatureForError ());
 143                 }
 144
 145                 public static void Error_ConstantCanBeInitializedWithNullOnly (Location loc, string name)
 146                 {
 147                         Report.Error (134, loc, "`{0}': the constant of reference type other than string can only be initialized with null",
 148                                 name);
 149                 }
 150
 151                 public static void Error_InvalidConstantType (Type t, Location loc)
 152                 {
 153                         Report.Error (283, loc, "The type `{0}' cannot be declared const", TypeManager.CSharpName (t));
 154                 }
 155
 156                 #region IConstant Members
 157
 158                 public bool ResolveValue ()
 159                 {
 160                         if (value != null)
 161                                 return true;
 162
 163                         SetMemberIsUsed ();
 164                         if (in_transit) {
 165                                 Error_CyclicDeclaration (this);
 166                                 // Suppress cyclic errors
 167                                 value = New.Constantify (MemberType);
 168                                 return false;
 169                         }
 170
 171                         in_transit = true;
 172                         // TODO: IResolveContext here
 173                         EmitContext ec = new EmitContext (this, Parent, Location, null, MemberType, ModFlags);
 174                         value = initializer.ResolveAsConstant (ec, this);
 175                         in_transit = false;
 176
 177                         if (value == null)
 178                                 return false;
 179
 180                         value = value.ImplicitConversionRequired (MemberType, Location);
 181                         if (value == null)
 182                                 return false;
 183
 184                         if (!MemberType.IsValueType && MemberType != TypeManager.string_type && !value.IsDefaultValue) {
 185                                 Error_ConstantCanBeInitializedWithNullOnly (Location, GetSignatureForError ());
 186                                 return false;
 187                         }
 188
 189                         return true;
 190                 }
 191
 192                 public Constant Value {
 193                         get {
 194                                 return value;
 195                         }
 196                 }
 197
 198                 #endregion
 199         }
 200
 201         public class ExternalConstant : IConstant
 202         {
 203                 FieldInfo fi;
 204                 Constant value;
 205
 206                 public ExternalConstant (FieldInfo fi)
 207                 {
 208                         this.fi = fi;
 209                 }
 210
 211                 private ExternalConstant (FieldInfo fi, Constant value):
 212                         this (fi)
 213                 {
 214                         this.value = value;
 215                 }
 216
 217                 //
 218                 // Decimal constants cannot be encoded in the constant blob, and thus are marked
 219                 // as IsInitOnly ('readonly' in C# parlance).  We get its value from the
 220                 // DecimalConstantAttribute metadata.
 221                 //
 222                 public static IConstant CreateDecimal (FieldInfo fi)
 223                 {
 224                         if (fi is FieldBuilder)
 225                                 return null;
 226
 227                         object[] attrs = fi.GetCustomAttributes (TypeManager.decimal_constant_attribute_type, false);
 228                         if (attrs.Length != 1)
 229                                 return null;
 230
 231                         IConstant ic = new ExternalConstant (fi,
 232                                 new DecimalConstant (((System.Runtime.CompilerServices.DecimalConstantAttribute) attrs [0]).Value, Location.Null));
 233
 234                         return ic;
 235                 }
 236
 237                 #region IConstant Members
 238
 239                 public void CheckObsoleteness (Location loc)
 240                 {
 241                         ObsoleteAttribute oa = AttributeTester.GetMemberObsoleteAttribute (fi);
 242                         if (oa == null) {
 243                                 return;
 244                         }
 245
 246                         AttributeTester.Report_ObsoleteMessage (oa, TypeManager.GetFullNameSignature (fi), loc);
 247                 }
 248
 249                 public bool ResolveValue ()
 250                 {
 251                         if (value != null)
 252                                 return true;
 253
 254                         if (fi.DeclaringType.IsEnum) {
 255                                 value = Expression.Constantify (fi.GetValue (fi), TypeManager.EnumToUnderlying (fi.FieldType));
 256                                 value = new EnumConstant (value, fi.DeclaringType);
 257                                 return true;
 258                         }
 259
 260                         value = Expression.Constantify (fi.GetValue (fi), fi.FieldType);
 261                         return true;
 262                 }
 263
 264                 public Constant Value {
 265                         get {
 266                                 return value;
 267                         }
 268                 }
 269
 270                 #endregion
 271         }
 272
 273 }