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