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 //
  13 // This is needed because the following situation arises:
  14 //
  15 //     The FieldBuilder is declared with the real type for an enumeration
  16 //
  17 //     When we attempt to set the value for the constant, the FieldBuilder.SetConstant
  18 //     function aborts because it requires its argument to be of the same type
  19 //
  20
  21 namespace Mono.CSharp {
  22
  23         using System;
  24         using System.Reflection;
  25         using System.Reflection.Emit;
  26         using System.Collections;
  27
  28         public class Const : FieldMember {
  29                 public Expression Expr;
  30                 EmitContext const_ec;
  31
  32                 bool resolved = false;
  33                 object ConstantValue = null;
  34
  35                 bool in_transit = false;
  36
  37                 public const int AllowedModifiers =
  38                         Modifiers.NEW |
  39                         Modifiers.PUBLIC |
  40                         Modifiers.PROTECTED |
  41                         Modifiers.INTERNAL |
  42                         Modifiers.PRIVATE;
  43
  44                 public Const (TypeContainer parent, Expression constant_type, string name,
  45                               Expression expr, int mod_flags, Attributes attrs, Location loc)
  46                         : base (parent, constant_type, mod_flags, AllowedModifiers,
  47                                 new MemberName (name), null, attrs, loc)
  48                 {
  49                         Expr = expr;
  50                         ModFlags |= Modifiers.STATIC;
  51                 }
  52
  53 #if DEBUG
  54                 void dump_tree (Type t)
  55                 {
  56                         Console.WriteLine ("Dumping hierarchy");
  57                         while (t != null){
  58                                 Console.WriteLine ("   " + t.FullName + " " +
  59                                         (t.GetType ().IsEnum ? "yes" : "no"));
  60                                 t = t.BaseType;
  61                         }
  62                 }
  63 #endif
  64
  65                 /// <summary>
  66                 ///   Defines the constant in the @parent
  67                 /// </summary>
  68                 public override bool Define ()
  69                 {
  70                         if (!base.Define ())
  71                                 return false;
  72
  73                         const_ec = new EmitContext (Parent, Location, null, MemberType, ModFlags);
  74
  75                         Type ttype = MemberType;
  76                         while (ttype.IsArray)
  77                             ttype = TypeManager.GetElementType (ttype);
  78
  79                         if (!TypeManager.IsBuiltinType(ttype) && (!ttype.IsSubclassOf(TypeManager.enum_type)) && !(Expr is NullLiteral)){
  80                                 Report.Error (
  81                                         -3, Location,
  82                                         "Constant type is not valid (only system types are allowed)");
  83                                 return false;
  84                         }
  85
  86                         FieldAttributes field_attr = FieldAttributes.Static | Modifiers.FieldAttr (ModFlags);
  87                         // I don't know why but they emit decimal constant as InitOnly
  88                         if (ttype == TypeManager.decimal_type) {
  89                                 field_attr |= FieldAttributes.InitOnly;
  90                         }
  91                         else {
  92                                 field_attr |= FieldAttributes.Literal;
  93                         }
  94
  95                         FieldBuilder = Parent.TypeBuilder.DefineField (Name, MemberType, field_attr);
  96
  97                         TypeManager.RegisterConstant (FieldBuilder, this);
  98
  99                         return true;
 100                 }
 101
 102                 //
 103                 // Changes the type of the constant expression `expr' to the Type `type'
 104                 // Returns null on failure.
 105                 //
 106                 public static Constant ChangeType (Location loc, Constant expr, Type type)
 107                 {
 108                         if (type == TypeManager.object_type)
 109                                 return expr;
 110
 111                         bool fail;
 112
 113                         // from the null type to any reference-type.
 114                         if (expr.Type == TypeManager.null_type && !type.IsValueType && !TypeManager.IsEnumType (type))
 115                                 return NullLiteral.Null;
 116
 117                         if (!Convert.ImplicitStandardConversionExists (Convert.ConstantEC, expr, type)){
 118                                 Convert.Error_CannotImplicitConversion (loc, expr.Type, type);
 119                                 return null;
 120                         }
 121
 122                         object constant_value = TypeManager.ChangeType (expr.GetValue (), type, out fail);
 123                         if (fail){
 124                                 Convert.Error_CannotImplicitConversion (loc, expr.Type, type);
 125
 126                                 //
 127                                 // We should always catch the error before this is ever
 128                                 // reached, by calling Convert.ImplicitStandardConversionExists
 129                                 //
 130                                 throw new Exception (
 131                                                      String.Format ("LookupConstantValue: This should never be reached {0} {1}", expr.Type, type));
 132                         }
 133
 134                         Constant retval;
 135                         if (type == TypeManager.int32_type)
 136                                 retval = new IntConstant ((int) constant_value);
 137                         else if (type == TypeManager.uint32_type)
 138                                 retval = new UIntConstant ((uint) constant_value);
 139                         else if (type == TypeManager.int64_type)
 140                                 retval = new LongConstant ((long) constant_value);
 141                         else if (type == TypeManager.uint64_type)
 142                                 retval = new ULongConstant ((ulong) constant_value);
 143                         else if (type == TypeManager.float_type)
 144                                 retval = new FloatConstant ((float) constant_value);
 145                         else if (type == TypeManager.double_type)
 146                                 retval = new DoubleConstant ((double) constant_value);
 147                         else if (type == TypeManager.string_type)
 148                                 retval = new StringConstant ((string) constant_value);
 149                         else if (type == TypeManager.short_type)
 150                                 retval = new ShortConstant ((short) constant_value);
 151                         else if (type == TypeManager.ushort_type)
 152                                 retval = new UShortConstant ((ushort) constant_value);
 153                         else if (type == TypeManager.sbyte_type)
 154                                 retval = new SByteConstant ((sbyte) constant_value);
 155                         else if (type == TypeManager.byte_type)
 156                                 retval = new ByteConstant ((byte) constant_value);
 157                         else if (type == TypeManager.char_type)
 158                                 retval = new CharConstant ((char) constant_value);
 159                         else if (type == TypeManager.bool_type)
 160                                 retval = new BoolConstant ((bool) constant_value);
 161                         else if (type == TypeManager.decimal_type)
 162                                 retval = new DecimalConstant ((decimal) constant_value);
 163                         else
 164                                 throw new Exception ("LookupConstantValue: Unhandled constant type: " + type);
 165
 166                         return retval;
 167                 }
 168
 169                 /// <summary>
 170                 ///  Looks up the value of a constant field. Defines it if it hasn't
 171                 ///  already been. Similar to LookupEnumValue in spirit.
 172                 /// </summary>
 173                 public bool LookupConstantValue (out object value)
 174                 {
 175                         if (resolved) {
 176                                 value = ConstantValue;
 177                                 return true;
 178                         }
 179
 180                         if (in_transit) {
 181                                 Report.Error (110, Location,
 182                                               "The evaluation of the constant value for `" +
 183                                               Name + "' involves a circular definition.");
 184                                 value = null;
 185                                 return false;
 186                         }
 187
 188                         in_transit = true;
 189                         int errors = Report.Errors;
 190
 191                         //
 192                         // We might have cleared Expr ourselves in a recursive definition
 193                         //
 194                         if (Expr == null){
 195                                 value = null;
 196                                 return false;
 197                         }
 198
 199                         Expr = Expr.Resolve (const_ec);
 200
 201                         in_transit = false;
 202
 203                         if (Expr == null) {
 204                                 if (errors == Report.Errors)
 205                                         Report.Error (150, Location, "A constant value is expected");
 206                                 value = null;
 207                                 return false;
 208                         }
 209
 210                         Expression real_expr = Expr;
 211
 212                         Constant ce = Expr as Constant;
 213                         if (ce == null){
 214                                 UnCheckedExpr un_expr = Expr as UnCheckedExpr;
 215                                 CheckedExpr ch_expr = Expr as CheckedExpr;
 216                                 EmptyCast ec_expr = Expr as EmptyCast;
 217
 218                                 if ((un_expr != null) && (un_expr.Expr is Constant))
 219                                         Expr = un_expr.Expr;
 220                                 else if ((ch_expr != null) && (ch_expr.Expr is Constant))
 221                                         Expr = ch_expr.Expr;
 222                                 else if ((ec_expr != null) && (ec_expr.Child is Constant))
 223                                         Expr = ec_expr.Child;
 224                                 else if (Expr is ArrayCreation){
 225                                         Report.Error (133, Location, "Arrays can not be constant");
 226                                 } else {
 227                                         if (errors == Report.Errors)
 228                                                 Report.Error (150, Location, "A constant value is expected");
 229                                         value = null;
 230                                         return false;
 231                                 }
 232
 233                                 ce = Expr as Constant;
 234                         }
 235
 236                         if (MemberType != real_expr.Type) {
 237                                 ce = ChangeType (Location, ce, MemberType);
 238                                 if (ce == null){
 239                                         value = null;
 240                                         return false;
 241                                 }
 242                                 Expr = ce;
 243                         }
 244                         ConstantValue = ce.GetValue ();
 245
 246                         if (MemberType.IsEnum){
 247                                 //
 248                                 // This sadly does not work for our user-defined enumerations types ;-(
 249                                 //
 250                                 try {
 251                                         ConstantValue = System.Enum.ToObject (
 252                                                 MemberType, ConstantValue);
 253                                 } catch (ArgumentException){
 254                                         Report.Error (
 255                                                 -16, Location,
 256                                                 ".NET SDK 1.0 does not permit to create the constant "+
 257                                                 " field from a user-defined enumeration");
 258                                 }
 259                         }
 260
 261                         if (ce is DecimalConstant) {
 262                                 Decimal d = ((DecimalConstant)ce).Value;
 263                                 int[] bits = Decimal.GetBits (d);
 264                                 object[] args = new object[] { (byte)(bits [3] >> 16), (byte)(bits [3] >> 31), (uint)bits [2], (uint)bits [1], (uint)bits [0] };
 265                                 CustomAttributeBuilder cab = new CustomAttributeBuilder (TypeManager.decimal_constant_attribute_ctor, args);
 266                                 FieldBuilder.SetCustomAttribute (cab);
 267                         }
 268                         else{
 269                                 FieldBuilder.SetConstant (ConstantValue);
 270                         }
 271
 272                         if (!TypeManager.RegisterFieldValue (FieldBuilder, ConstantValue))
 273                                 throw new Exception ("Cannot register const value");
 274
 275                         value = ConstantValue;
 276                         resolved = true;
 277                         return true;
 278                 }
 279
 280
 281                 /// <summary>
 282                 ///  Emits the field value by evaluating the expression
 283                 /// </summary>
 284                 public override void Emit ()
 285                 {
 286                         object value;
 287                         LookupConstantValue (out value);
 288
 289                         if (OptAttributes != null) {
 290                                 OptAttributes.Emit (const_ec, this);
 291                         }
 292
 293                         base.Emit ();
 294                 }
 295         }
 296 }
 297
 298