mcs/mcs/const.cs

   1 //
   2 // const.cs: Constant declarations.
   3 //
   4 // Author:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //
   7 // (C) 2001 Ximian, Inc.
   8 //
   9 //
  10
  11 //
  12 // This is needed because the following situation arises:
  13 //
  14 //     The FieldBuilder is declared with the real type for an enumeration
  15 //
  16 //     When we attempt to set the value for the constant, the FieldBuilder.SetConstant
  17 //     function aborts because it requires its argument to be of the same type
  18 //
  19
  20 namespace Mono.CSharp {
  21
  22         using System;
  23         using System.Reflection;
  24         using System.Reflection.Emit;
  25         using System.Collections;
  26
  27         public class Const : FieldBase {
  28                 public Expression Expr;
  29                 EmitContext const_ec;
  30
  31                 bool resolved = false;
  32                 object ConstantValue = null;
  33                 Type type;
  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, name,
  47                                 null, attrs, loc)
  48                 {
  49                         Expr = expr;
  50                 }
  51
  52                 public FieldAttributes FieldAttr {
  53                         get {
  54                                 return FieldAttributes.Literal | FieldAttributes.Static |
  55                                         Modifiers.FieldAttr (ModFlags) ;
  56                         }
  57                 }
  58
  59 #if DEBUG
  60                 void dump_tree (Type t)
  61                 {
  62                         Console.WriteLine ("Dumping hierarchy");
  63                         while (t != null){
  64                                 Console.WriteLine ("   " + t.FullName + " " +
  65                                         (t.GetType ().IsEnum ? "yes" : "no"));
  66                                 t = t.BaseType;
  67                         }
  68                 }
  69 #endif
  70
  71                 /// <summary>
  72                 ///   Defines the constant in the @parent
  73                 /// </summary>
  74                 public override bool Define ()
  75                 {
  76                         type = Parent.ResolveType (Type, false, Location);
  77
  78                         if (type == null)
  79                                 return false;
  80
  81                         const_ec = new EmitContext (Parent, Location, null, type, ModFlags);
  82
  83                         Type ttype = type;
  84                         while (ttype.IsArray)
  85                             ttype = TypeManager.GetElementType (ttype);
  86
  87                         if (!TypeManager.IsBuiltinType (ttype) &&
  88                             (!ttype.IsSubclassOf (TypeManager.enum_type))) {
  89                                 Report.Error (
  90                                         -3, Location,
  91                                         "Constant type is not valid (only system types are allowed)");
  92                                 return false;
  93                         }
  94
  95                         if (!CheckBase ())
  96                                 return false;
  97
  98                         FieldBuilder = Parent.TypeBuilder.DefineField (Name, type, FieldAttr);
  99
 100                         TypeManager.RegisterConstant (FieldBuilder, this);
 101
 102                         return true;
 103                 }
 104
 105                 //
 106                 // Changes the type of the constant expression `expr' to the Type `type'
 107                 // Returns null on failure.
 108                 //
 109                 public static Constant ChangeType (Location loc, Constant expr, Type type)
 110                 {
 111                         if (type == TypeManager.object_type)
 112                                 return expr;
 113
 114                         bool fail;
 115
 116                         // from the null type to any reference-type.
 117                         if (expr is NullLiteral && !type.IsValueType && !TypeManager.IsEnumType (type))
 118                                 return NullLiteral.Null;
 119
 120                         if (!Convert.ImplicitStandardConversionExists (expr, type)){
 121                                 Convert.Error_CannotImplicitConversion (loc, expr.Type, type);
 122                                 return null;
 123                         }
 124
 125                         object constant_value = TypeManager.ChangeType (expr.GetValue (), type, out fail);
 126                         if (fail){
 127                                 Convert.Error_CannotImplicitConversion (loc, expr.Type, type);
 128
 129                                 //
 130                                 // We should always catch the error before this is ever
 131                                 // reached, by calling Convert.ImplicitStandardConversionExists
 132                                 //
 133                                 throw new Exception (
 134                                                      String.Format ("LookupConstantValue: This should never be reached {0} {1}", expr.Type, type));
 135                         }
 136
 137                         Constant retval;
 138                         if (type == TypeManager.int32_type)
 139                                 retval = new IntConstant ((int) constant_value);
 140                         else if (type == TypeManager.uint32_type)
 141                                 retval = new UIntConstant ((uint) constant_value);
 142                         else if (type == TypeManager.int64_type)
 143                                 retval = new LongConstant ((long) constant_value);
 144                         else if (type == TypeManager.uint64_type)
 145                                 retval = new ULongConstant ((ulong) constant_value);
 146                         else if (type == TypeManager.float_type)
 147                                 retval = new FloatConstant ((float) constant_value);
 148                         else if (type == TypeManager.double_type)
 149                                 retval = new DoubleConstant ((double) constant_value);
 150                         else if (type == TypeManager.string_type)
 151                                 retval = new StringConstant ((string) constant_value);
 152                         else if (type == TypeManager.short_type)
 153                                 retval = new ShortConstant ((short) constant_value);
 154                         else if (type == TypeManager.ushort_type)
 155                                 retval = new UShortConstant ((ushort) constant_value);
 156                         else if (type == TypeManager.sbyte_type)
 157                                 retval = new SByteConstant ((sbyte) constant_value);
 158                         else if (type == TypeManager.byte_type)
 159                                 retval = new ByteConstant ((byte) constant_value);
 160                         else if (type == TypeManager.char_type)
 161                                 retval = new CharConstant ((char) constant_value);
 162                         else if (type == TypeManager.bool_type)
 163                                 retval = new BoolConstant ((bool) constant_value);
 164                         else
 165                                 throw new Exception ("LookupConstantValue: Unhandled constant type: " + type);
 166
 167                         return retval;
 168                 }
 169
 170                 /// <summary>
 171                 ///  Looks up the value of a constant field. Defines it if it hasn't
 172                 ///  already been. Similar to LookupEnumValue in spirit.
 173                 /// </summary>
 174                 public bool LookupConstantValue (out object value)
 175                 {
 176                         if (resolved) {
 177                                 value = ConstantValue;
 178                                 return true;
 179                         }
 180
 181                         if (in_transit) {
 182                                 Report.Error (110, Location,
 183                                               "The evaluation of the constant value for `" +
 184                                               Name + "' involves a circular definition.");
 185                                 value = null;
 186                                 return false;
 187                         }
 188
 189                         in_transit = true;
 190                         int errors = Report.Errors;
 191
 192                         //
 193                         // We might have cleared Expr ourselves in a recursive definition
 194                         //
 195                         if (Expr == null){
 196                                 value = null;
 197                                 return false;
 198                         }
 199
 200                         Expr = Expr.Resolve (const_ec);
 201
 202                         in_transit = false;
 203
 204                         if (Expr == null) {
 205                                 if (errors == Report.Errors)
 206                                         Report.Error (150, Location, "A constant value is expected");
 207                                 value = null;
 208                                 return false;
 209                         }
 210
 211                         Expression real_expr = Expr;
 212
 213                         Constant ce = Expr as Constant;
 214                         if (ce == null){
 215                                 UnCheckedExpr un_expr = Expr as UnCheckedExpr;
 216                                 CheckedExpr ch_expr = Expr as CheckedExpr;
 217                                 EmptyCast ec_expr = Expr as EmptyCast;
 218
 219                                 if ((un_expr != null) && (un_expr.Expr is Constant))
 220                                         Expr = un_expr.Expr;
 221                                 else if ((ch_expr != null) && (ch_expr.Expr is Constant))
 222                                         Expr = ch_expr.Expr;
 223                                 else if ((ec_expr != null) && (ec_expr.Child is Constant))
 224                                         Expr = ec_expr.Child;
 225                                 else if (Expr is ArrayCreation) {
 226                                         ArrayCreation ac = (ArrayCreation) Expr;
 227
 228                                         Expr = ac.TurnIntoConstant ();
 229                                         if (Expr == null){
 230                                                 Report.Error (150, Location, "A constant value is expected");
 231                                                 value = null;
 232                                                 return false;
 233                                         }
 234                                 } else {
 235                                         if (errors == Report.Errors)
 236                                                 Report.Error (150, Location, "A constant value is expected");
 237                                         value = null;
 238                                         return false;
 239                                 }
 240
 241                                 ce = Expr as Constant;
 242                         }
 243
 244                         if (type != real_expr.Type) {
 245                                 ce = ChangeType (Location, ce, type);
 246                                 if (ce == null){
 247                                         value = null;
 248                                         return false;
 249                                 }
 250                                 Expr = ce;
 251                         }
 252                         ConstantValue = ce.GetValue ();
 253
 254                         if (type.IsEnum){
 255                                 //
 256                                 // This sadly does not work for our user-defined enumerations types ;-(
 257                                 //
 258                                 try {
 259                                         ConstantValue = System.Enum.ToObject (
 260                                                 type, ConstantValue);
 261                                 } catch (ArgumentException){
 262                                         Report.Error (
 263                                                 -16, Location,
 264                                                 ".NET SDK 1.0 does not permit to create the constant "+
 265                                                 " field from a user-defined enumeration");
 266                                 }
 267                         }
 268
 269                         FieldBuilder.SetConstant (ConstantValue);
 270
 271                         if (!TypeManager.RegisterFieldValue (FieldBuilder, ConstantValue))
 272                                 throw new Exception ("Cannot register const value");
 273
 274                         value = ConstantValue;
 275                         resolved = true;
 276                         return true;
 277                 }
 278
 279
 280                 /// <summary>
 281                 ///  Emits the field value by evaluating the expression
 282                 /// </summary>
 283                 public override void Emit ()
 284                 {
 285                         object value;
 286                         LookupConstantValue (out value);
 287
 288                         if (OptAttributes != null) {
 289                                 OptAttributes.Emit (const_ec, this);
 290                         }
 291
 292                         base.Emit ();
 293                 }
 294         }
 295 }
 296
 297