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
  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 (Parent.PartialContainer.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                         if (!IsConstantTypeValid (ttype)) {
  70                                 Error_InvalidConstantType (ttype, Location);
  71                                 return false;
  72                         }
  73
  74                         while (ttype.IsArray)
  75                             ttype = TypeManager.GetElementType (ttype);
  76
  77                         FieldAttributes field_attr = FieldAttributes.Static | Modifiers.FieldAttr (ModFlags);
  78                         // Decimals cannot be emitted into the constant blob.  So, convert to 'readonly'.
  79                         if (ttype == TypeManager.decimal_type) {
  80                                 field_attr |= FieldAttributes.InitOnly;
  81                                 Parent.PartialContainer.RegisterFieldForInitialization (this);
  82                         } else {
  83                                 field_attr |= FieldAttributes.Literal;
  84                         }
  85
  86                         FieldBuilder = Parent.TypeBuilder.DefineField (Name, MemberType, field_attr);
  87
  88                         TypeManager.RegisterConstant (FieldBuilder, this);
  89
  90                         return true;
  91                 }
  92
  93                 public static bool IsConstantTypeValid (Type t)
  94                 {
  95                         if (TypeManager.IsBuiltinOrEnum (t))
  96                                 return true;
  97
  98                         if (t.IsPointer || t.IsValueType)
  99                                 return false;
 100
 101                         if (TypeManager.IsGenericParameter (t))
 102                                 return false;
 103
 104                         return true;
 105                 }
 106
 107                 /// <summary>
 108                 ///  Emits the field value by evaluating the expression
 109                 /// </summary>
 110                 public override void Emit ()
 111                 {
 112                         if (!ResolveValue ())
 113                                 return;
 114
 115                         if (value.Type == TypeManager.decimal_type) {
 116                                 Decimal d = ((DecimalConstant)value).Value;
 117                                 int[] bits = Decimal.GetBits (d);
 118                                 object[] args = new object[] { (byte)(bits [3] >> 16), (byte)(bits [3] >> 31), (uint)bits [2], (uint)bits [1], (uint)bits [0] };
 119                                 CustomAttributeBuilder cab = new CustomAttributeBuilder (TypeManager.decimal_constant_attribute_ctor, args);
 120                                 FieldBuilder.SetCustomAttribute (cab);
 121                         }
 122                         else{
 123                                 FieldBuilder.SetConstant (value.GetTypedValue ());
 124                         }
 125
 126                         base.Emit ();
 127                 }
 128
 129                 public static void Error_ExpressionMustBeConstant (Location loc, string e_name)
 130                 {
 131                         Report.Error (133, loc, "The expression being assigned to `{0}' must be constant", e_name);
 132                 }
 133
 134                 public static void Error_CyclicDeclaration (MemberCore mc)
 135                 {
 136                         Report.Error (110, mc.Location, "The evaluation of the constant value for `{0}' involves a circular definition",
 137                                 mc.GetSignatureForError ());
 138                 }
 139
 140                 public static void Error_ConstantCanBeInitializedWithNullOnly (Location loc, string name)
 141                 {
 142                         Report.Error (134, loc, "`{0}': the constant of reference type other than string can only be initialized with null",
 143                                 name);
 144                 }
 145
 146                 public static void Error_InvalidConstantType (Type t, Location loc)
 147                 {
 148                         Report.Error (283, loc, "The type `{0}' cannot be declared const", TypeManager.CSharpName (t));
 149                 }
 150
 151                 #region IConstant Members
 152
 153                 public bool ResolveValue ()
 154                 {
 155                         if (value != null)
 156                                 return true;
 157
 158                         SetMemberIsUsed ();
 159                         if (in_transit) {
 160                                 Error_CyclicDeclaration (this);
 161                                 // Suppress cyclic errors
 162                                 value = New.Constantify (MemberType);
 163                                 return false;
 164                         }
 165
 166                         in_transit = true;
 167                         // TODO: IResolveContext here
 168                         EmitContext ec = new EmitContext (this, Parent, Location, null, MemberType, ModFlags);
 169                         value = initializer.ResolveAsConstant (ec, this);
 170                         in_transit = false;
 171
 172                         if (value == null)
 173                                 return false;
 174
 175                         value = value.ImplicitConversionRequired (MemberType, Location);
 176                         if (value == null)
 177                                 return false;
 178
 179                         if (!MemberType.IsValueType && MemberType != TypeManager.string_type && !value.IsDefaultValue) {
 180                                 Error_ConstantCanBeInitializedWithNullOnly (Location, GetSignatureForError ());
 181                                 return false;
 182                         }
 183
 184                         return true;
 185                 }
 186
 187                 public Constant Value {
 188                         get {
 189                                 return value;
 190                         }
 191                 }
 192
 193                 #endregion
 194         }
 195
 196         public class ExternalConstant : IConstant
 197         {
 198                 FieldInfo fi;
 199                 Constant value;
 200
 201                 public ExternalConstant (FieldInfo fi)
 202                 {
 203                         this.fi = fi;
 204                 }
 205
 206                 private ExternalConstant (FieldInfo fi, Constant value):
 207                         this (fi)
 208                 {
 209                         this.value = value;
 210                 }
 211
 212                 //
 213                 // Decimal constants cannot be encoded in the constant blob, and thus are marked
 214                 // as IsInitOnly ('readonly' in C# parlance).  We get its value from the
 215                 // DecimalConstantAttribute metadata.
 216                 //
 217                 public static IConstant CreateDecimal (FieldInfo fi)
 218                 {
 219                         if (fi is FieldBuilder)
 220                                 return null;
 221
 222                         object[] attrs = fi.GetCustomAttributes (TypeManager.decimal_constant_attribute_type, false);
 223                         if (attrs.Length != 1)
 224                                 return null;
 225
 226                         IConstant ic = new ExternalConstant (fi,
 227                                 new DecimalConstant (((System.Runtime.CompilerServices.DecimalConstantAttribute) attrs [0]).Value, Location.Null));
 228
 229                         return ic;
 230                 }
 231
 232                 #region IConstant Members
 233
 234                 public void CheckObsoleteness (Location loc)
 235                 {
 236                         ObsoleteAttribute oa = AttributeTester.GetMemberObsoleteAttribute (fi);
 237                         if (oa == null) {
 238                                 return;
 239                         }
 240
 241                         AttributeTester.Report_ObsoleteMessage (oa, TypeManager.GetFullNameSignature (fi), loc);
 242                 }
 243
 244                 public bool ResolveValue ()
 245                 {
 246                         if (value != null)
 247                                 return true;
 248
 249                         if (fi.DeclaringType.IsEnum) {
 250                                 value = Expression.Constantify (fi.GetValue (fi), TypeManager.EnumToUnderlying (fi.FieldType));
 251                                 value = new EnumConstant (value, fi.DeclaringType);
 252                                 return true;
 253                         }
 254
 255                         value = Expression.Constantify (fi.GetValue (fi), fi.FieldType);
 256                         return true;
 257                 }
 258
 259                 public Constant Value {
 260                         get {
 261                                 return value;
 262                         }
 263                 }
 264
 265                 #endregion
 266         }
 267
 268 }