mcs/gmcs/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                 object ConstantValue = null;
  32                 Type type;
  33
  34                 bool in_transit = false;
  35
  36                 public const int AllowedModifiers =
  37                         Modifiers.NEW |
  38                         Modifiers.PUBLIC |
  39                         Modifiers.PROTECTED |
  40                         Modifiers.INTERNAL |
  41                         Modifiers.PRIVATE;
  42
  43                 public Const (Expression constant_type, string name, Expression expr, int mod_flags,
  44                               Attributes attrs, Location loc)
  45                         : base (constant_type, mod_flags, AllowedModifiers, name, null, attrs, loc)
  46                 {
  47                         Expr = expr;
  48                 }
  49
  50                 public FieldAttributes FieldAttr {
  51                         get {
  52                                 return FieldAttributes.Literal | FieldAttributes.Static |
  53                                         Modifiers.FieldAttr (ModFlags) ;
  54                         }
  55                 }
  56
  57 #if DEBUG
  58                 void dump_tree (Type t)
  59                 {
  60                         Console.WriteLine ("Dumping hierarchy");
  61                         while (t != null){
  62                                 Console.WriteLine ("   " + t.FullName + " " +
  63                                         (t.GetType ().IsEnum ? "yes" : "no"));
  64                                 t = t.BaseType;
  65                         }
  66                 }
  67 #endif
  68
  69                 /// <summary>
  70                 ///   Defines the constant in the @parent
  71                 /// </summary>
  72                 public override bool Define (TypeContainer parent)
  73                 {
  74                         type = parent.ResolveType (Type, false, Location);
  75
  76                         if (type == null)
  77                                 return false;
  78
  79                         const_ec = new EmitContext (parent, Location, null, type, ModFlags);
  80
  81                         if (!TypeManager.IsBuiltinType (type) &&
  82                             (!type.IsSubclassOf (TypeManager.enum_type))) {
  83                                 Report.Error (
  84                                         -3, Location,
  85                                         "Constant type is not valid (only system types are allowed)");
  86                                 return false;
  87                         }
  88
  89                         Type ptype = parent.TypeBuilder.BaseType;
  90
  91                         if (ptype != null) {
  92                                 MemberList list = TypeContainer.FindMembers (
  93                                         ptype, MemberTypes.Field, BindingFlags.Public,
  94                                         System.Type.FilterName, Name);
  95
  96                                 if (list.Count == 0)
  97                                         if ((ModFlags & Modifiers.NEW) != 0)
  98                                                 WarningNotHiding (parent);
  99
 100                         } else if ((ModFlags & Modifiers.NEW) != 0)
 101                                 WarningNotHiding (parent);
 102
 103                         FieldBuilder = parent.TypeBuilder.DefineField (Name, type, FieldAttr);
 104
 105                         TypeManager.RegisterConstant (FieldBuilder, this);
 106
 107                         return true;
 108                 }
 109
 110                 //
 111                 // Changes the type of the constant expression `expr' to the Type `type'
 112                 // Returns null on failure.
 113                 //
 114                 public static Constant ChangeType (Location loc, Constant expr, Type type)
 115                 {
 116                         bool fail;
 117
 118                         // from the null type to any reference-type.
 119                         if (expr is NullLiteral && !type.IsValueType && !TypeManager.IsEnumType (type))
 120                                 return NullLiteral.Null;
 121
 122                         if (!Convert.ImplicitStandardConversionExists (expr, type)){
 123                                 Convert.Error_CannotImplicitConversion (loc, expr.Type, type);
 124                                 return null;
 125                         }
 126
 127                         object constant_value = TypeManager.ChangeType (expr.GetValue (), type, out fail);
 128                         if (fail){
 129                                 Convert.Error_CannotImplicitConversion (loc, expr.Type, type);
 130
 131                                 //
 132                                 // We should always catch the error before this is ever
 133                                 // reached, by calling Convert.ImplicitStandardConversionExists
 134                                 //
 135                                 throw new Exception (
 136                                                      String.Format ("LookupConstantValue: This should never be reached {0} {1}", expr.Type, type));
 137                         }
 138
 139                         Constant retval;
 140                         if (type == TypeManager.int32_type)
 141                                 retval = new IntConstant ((int) constant_value);
 142                         else if (type == TypeManager.uint32_type)
 143                                 retval = new UIntConstant ((uint) constant_value);
 144                         else if (type == TypeManager.int64_type)
 145                                 retval = new LongConstant ((long) constant_value);
 146                         else if (type == TypeManager.uint64_type)
 147                                 retval = new ULongConstant ((ulong) constant_value);
 148                         else if (type == TypeManager.float_type)
 149                                 retval = new FloatConstant ((float) constant_value);
 150                         else if (type == TypeManager.double_type)
 151                                 retval = new DoubleConstant ((double) constant_value);
 152                         else if (type == TypeManager.string_type)
 153                                 retval = new StringConstant ((string) constant_value);
 154                         else if (type == TypeManager.short_type)
 155                                 retval = new ShortConstant ((short) constant_value);
 156                         else if (type == TypeManager.ushort_type)
 157                                 retval = new UShortConstant ((ushort) constant_value);
 158                         else if (type == TypeManager.sbyte_type)
 159                                 retval = new SByteConstant ((sbyte) constant_value);
 160                         else if (type == TypeManager.byte_type)
 161                                 retval = new ByteConstant ((byte) constant_value);
 162                         else if (type == TypeManager.char_type)
 163                                 retval = new CharConstant ((char) constant_value);
 164                         else if (type == TypeManager.bool_type)
 165                                 retval = new BoolConstant ((bool) constant_value);
 166                         else
 167                                 throw new Exception ("LookupConstantValue: Unhandled constant type: " + type);
 168
 169                         return retval;
 170                 }
 171
 172                 /// <summary>
 173                 ///  Looks up the value of a constant field. Defines it if it hasn't
 174                 ///  already been. Similar to LookupEnumValue in spirit.
 175                 /// </summary>
 176                 public object LookupConstantValue ()
 177                 {
 178                         if (ConstantValue != null)
 179                                 return ConstantValue;
 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                                 return null;
 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                                 return null;
 196
 197                         Expr = Expr.Resolve (const_ec);
 198
 199                         in_transit = false;
 200
 201                         if (Expr == null) {
 202                                 if (errors == Report.Errors)
 203                                         Report.Error (150, Location, "A constant value is expected");
 204                                 return null;
 205                         }
 206
 207                         Constant ce = Expr as Constant;
 208                         if (ce == null){
 209                                 UnCheckedExpr un_expr = Expr as UnCheckedExpr;
 210                                 CheckedExpr ch_expr = Expr as CheckedExpr;
 211
 212                                 if ((un_expr != null) && (un_expr.Expr is Constant))
 213                                         Expr = un_expr.Expr;
 214                                 else if ((ch_expr != null) && (ch_expr.Expr is Constant))
 215                                         Expr = ch_expr.Expr;
 216                                 else {
 217                                         if (errors == Report.Errors)
 218                                                 Report.Error (150, Location, "A constant value is expected");
 219                                         return null;
 220                                 }
 221                         }
 222
 223                         if (type != ce.Type) {
 224                                 ce = ChangeType (Location, ce, type);
 225                                 if (ce == null)
 226                                         return null;
 227                                 Expr = ce;
 228                         }
 229                         ConstantValue = ce.GetValue ();
 230
 231                         if (type.IsEnum){
 232                                 //
 233                                 // This sadly does not work for our user-defined enumerations types ;-(
 234                                 //
 235                                 try {
 236                                         ConstantValue = System.Enum.ToObject (
 237                                                 type, ConstantValue);
 238                                 } catch (ArgumentException){
 239                                         Report.Error (
 240                                                 -16, Location,
 241                                                 ".NET SDK 1.0 does not permit to create the constant "+
 242                                                 " field from a user-defined enumeration");
 243                                 }
 244                         }
 245
 246                         FieldBuilder.SetConstant (ConstantValue);
 247
 248                         if (!TypeManager.RegisterFieldValue (FieldBuilder, ConstantValue))
 249                                 return null;
 250
 251                         return ConstantValue;
 252                 }
 253
 254
 255                 /// <summary>
 256                 ///  Emits the field value by evaluating the expression
 257                 /// </summary>
 258                 public void Emit (TypeContainer parent)
 259                 {
 260                         LookupConstantValue ();
 261
 262                         return;
 263                 }
 264         }
 265 }
 266
 267