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 CreateConstantReference (Location loc);
  24         }
  25
  26         public class Const : FieldBase, IConstant {
  27                 protected Constant value;
  28                 bool in_transit;
  29                 bool resolved;
  30                 bool define_called;
  31
  32                 public const int AllowedModifiers =
  33                         Modifiers.NEW |
  34                         Modifiers.PUBLIC |
  35                         Modifiers.PROTECTED |
  36                         Modifiers.INTERNAL |
  37                         Modifiers.PRIVATE;
  38
  39                 public Const (DeclSpace parent, Expression constant_type, string name,
  40                               Expression expr, int mod_flags, Attributes attrs, Location loc)
  41                         : base (parent, constant_type, mod_flags, AllowedModifiers,
  42                                 new MemberName (name, loc), attrs)
  43                 {
  44                         initializer = expr;
  45                         ModFlags |= Modifiers.STATIC;
  46                 }
  47
  48                 protected override bool CheckBase ()
  49                 {
  50                         // Constant.Define can be called when the parent type hasn't yet been populated
  51                         // and it's base types need not have been populated.  So, we defer this check
  52                         // to the second time Define () is called on this member.
  53                         if (Parent.PartialContainer.BaseCache == null)
  54                                 return true;
  55                         return base.CheckBase ();
  56                 }
  57
  58                 /// <summary>
  59                 ///   Defines the constant in the @parent
  60                 /// </summary>
  61                 public override bool Define ()
  62                 {
  63                         // Because constant define can be called from other class
  64                         if (define_called) {
  65                                 CheckBase ();
  66                                 return FieldBuilder != null;
  67                         }
  68
  69                         define_called = true;
  70
  71                         if (!base.Define ())
  72                                 return false;
  73
  74                         Type ttype = MemberType;
  75                         if (!IsConstantTypeValid (ttype)) {
  76                                 Error_InvalidConstantType (ttype, Location);
  77                                 return false;
  78                         }
  79
  80                         // If the constant is private then we don't need any field the
  81                         // value is already inlined and cannot be referenced
  82                         //if ((ModFlags & Modifiers.PRIVATE) != 0 && RootContext.Optimize)
  83                         //      return true;
  84
  85                         while (ttype.IsArray)
  86                                 ttype = TypeManager.GetElementType (ttype);
  87
  88                         FieldAttributes field_attr = FieldAttributes.Static | Modifiers.FieldAttr (ModFlags);
  89                         // Decimals cannot be emitted into the constant blob.  So, convert to 'readonly'.
  90                         if (ttype == TypeManager.decimal_type) {
  91                                 field_attr |= FieldAttributes.InitOnly;
  92                         } else {
  93                                 field_attr |= FieldAttributes.Literal;
  94                         }
  95
  96                         FieldBuilder = Parent.TypeBuilder.DefineField (Name, MemberType, field_attr);
  97                         TypeManager.RegisterConstant (FieldBuilder, this);
  98                         Parent.MemberCache.AddMember (FieldBuilder, this);
  99
 100                         if (ttype == TypeManager.decimal_type)
 101                                 Parent.PartialContainer.RegisterFieldForInitialization (this,
 102                                         new FieldInitializer (FieldBuilder, initializer));
 103
 104                         return true;
 105                 }
 106
 107                 public static bool IsConstantTypeValid (Type t)
 108                 {
 109                         if (TypeManager.IsBuiltinOrEnum (t))
 110                                 return true;
 111
 112                         if (t.IsPointer || t.IsValueType)
 113                                 return false;
 114
 115                         if (TypeManager.IsGenericParameter (t))
 116                                 return false;
 117
 118                         return true;
 119                 }
 120
 121                 /// <summary>
 122                 ///  Emits the field value by evaluating the expression
 123                 /// </summary>
 124                 public override void Emit ()
 125                 {
 126                         if (!ResolveValue ())
 127                                 return;
 128
 129                         if (FieldBuilder == null)
 130                                 return;
 131
 132                         if (value.Type == TypeManager.decimal_type) {
 133                                 Decimal d = ((DecimalConstant)value).Value;
 134                                 int[] bits = Decimal.GetBits (d);
 135                                 object[] args = new object[] { (byte)(bits [3] >> 16), (byte)(bits [3] >> 31), (uint)bits [2], (uint)bits [1], (uint)bits [0] };
 136                                 CustomAttributeBuilder cab = new CustomAttributeBuilder (TypeManager.decimal_constant_attribute_ctor, args);
 137                                 FieldBuilder.SetCustomAttribute (cab);
 138                         }
 139                         else{
 140                                 FieldBuilder.SetConstant (value.GetTypedValue ());
 141                         }
 142
 143                         base.Emit ();
 144                 }
 145
 146                 public static void Error_ExpressionMustBeConstant (Location loc, string e_name)
 147                 {
 148                         Report.Error (133, loc, "The expression being assigned to `{0}' must be constant", e_name);
 149                 }
 150
 151                 public static void Error_CyclicDeclaration (MemberCore mc)
 152                 {
 153                         Report.Error (110, mc.Location, "The evaluation of the constant value for `{0}' involves a circular definition",
 154                                 mc.GetSignatureForError ());
 155                 }
 156
 157                 public static void Error_ConstantCanBeInitializedWithNullOnly (Location loc, string name)
 158                 {
 159                         Report.Error (134, loc, "`{0}': the constant of reference type other than string can only be initialized with null",
 160                                 name);
 161                 }
 162
 163                 public static void Error_InvalidConstantType (Type t, Location loc)
 164                 {
 165                         Report.Error (283, loc, "The type `{0}' cannot be declared const", TypeManager.CSharpName (t));
 166                 }
 167
 168                 #region IConstant Members
 169
 170                 public bool ResolveValue ()
 171                 {
 172                         if (resolved)
 173                                 return value != null;
 174
 175                         SetMemberIsUsed ();
 176                         if (in_transit) {
 177                                 Error_CyclicDeclaration (this);
 178                                 // Suppress cyclic errors
 179                                 value = New.Constantify (MemberType);
 180                                 resolved = true;
 181                                 return false;
 182                         }
 183
 184                         in_transit = true;
 185                         // TODO: IResolveContext here
 186                         EmitContext ec = new EmitContext (
 187                                 this, Parent, Location, null, MemberType, ModFlags);
 188                         ec.InEnumContext = this is EnumMember;
 189                         ec.IsAnonymousMethodAllowed = false;
 190                         value = DoResolveValue (ec);
 191                         in_transit = false;
 192                         resolved = true;
 193                         return value != null;
 194                 }
 195
 196                 protected virtual Constant DoResolveValue (EmitContext ec)
 197                 {
 198                         Constant value = initializer.ResolveAsConstant (ec, this);
 199                         if (value == null)
 200                                 return null;
 201
 202                         Constant c = value.ConvertImplicitly (MemberType);
 203                         if (c == null) {
 204                                 if (!MemberType.IsValueType && MemberType != TypeManager.string_type && !value.IsDefaultValue)
 205                                         Error_ConstantCanBeInitializedWithNullOnly (Location, GetSignatureForError ());
 206                                 else
 207                                         value.Error_ValueCannotBeConverted (null, Location, MemberType, false);
 208                         }
 209
 210                         return c;
 211                 }
 212
 213                 public virtual Constant CreateConstantReference (Location loc)
 214                 {
 215                         if (value == null)
 216                                 return null;
 217
 218                         return Constant.CreateConstant (value.Type, value.GetValue(), loc);
 219                 }
 220
 221                 #endregion
 222         }
 223
 224         public class ExternalConstant : IConstant
 225         {
 226                 FieldInfo fi;
 227                 object value;
 228
 229                 public ExternalConstant (FieldInfo fi)
 230                 {
 231                         this.fi = fi;
 232                 }
 233
 234                 private ExternalConstant (FieldInfo fi, object value):
 235                         this (fi)
 236                 {
 237                         this.value = value;
 238                 }
 239
 240                 //
 241                 // Decimal constants cannot be encoded in the constant blob, and thus are marked
 242                 // as IsInitOnly ('readonly' in C# parlance).  We get its value from the
 243                 // DecimalConstantAttribute metadata.
 244                 //
 245                 public static IConstant CreateDecimal (FieldInfo fi)
 246                 {
 247                         if (fi is FieldBuilder)
 248                                 return null;
 249
 250                         object[] attrs = fi.GetCustomAttributes (TypeManager.decimal_constant_attribute_type, false);
 251                         if (attrs.Length != 1)
 252                                 return null;
 253
 254                         IConstant ic = new ExternalConstant (fi,
 255                                 ((System.Runtime.CompilerServices.DecimalConstantAttribute) attrs [0]).Value);
 256
 257                         return ic;
 258                 }
 259
 260                 #region IConstant Members
 261
 262                 public void CheckObsoleteness (Location loc)
 263                 {
 264                         ObsoleteAttribute oa = AttributeTester.GetMemberObsoleteAttribute (fi);
 265                         if (oa == null) {
 266                                 return;
 267                         }
 268
 269                         AttributeTester.Report_ObsoleteMessage (oa, TypeManager.GetFullNameSignature (fi), loc);
 270                 }
 271
 272                 public bool ResolveValue ()
 273                 {
 274                         if (value != null)
 275                                 return true;
 276
 277                         value = fi.GetValue (fi);
 278                         return true;
 279                 }
 280
 281                 public Constant CreateConstantReference (Location loc)
 282                 {
 283                         return Constant.CreateConstant (fi.FieldType, value, loc);
 284                 }
 285
 286                 #endregion
 287         }
 288
 289 }