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
  99                         if (ttype == TypeManager.decimal_type)
 100                                 Parent.PartialContainer.RegisterFieldForInitialization (this,
 101                                         new FieldInitializer (FieldBuilder, initializer, Parent));
 102
 103                         return true;
 104                 }
 105
 106                 public static bool IsConstantTypeValid (Type t)
 107                 {
 108                         if (TypeManager.IsBuiltinOrEnum (t))
 109                                 return true;
 110
 111                         if (t.IsPointer || t.IsValueType)
 112                                 return false;
 113
 114                         if (TypeManager.IsGenericParameter (t))
 115                                 return false;
 116
 117                         return true;
 118                 }
 119
 120                 /// <summary>
 121                 ///  Emits the field value by evaluating the expression
 122                 /// </summary>
 123                 public override void Emit ()
 124                 {
 125                         if (!ResolveValue ())
 126                                 return;
 127
 128                         if (FieldBuilder == null)
 129                                 return;
 130
 131                         if (value.Type == TypeManager.decimal_type) {
 132                                 Decimal d = ((DecimalConstant)value).Value;
 133                                 int[] bits = Decimal.GetBits (d);
 134                                 object[] args = new object[] { (byte)(bits [3] >> 16), (byte)(bits [3] >> 31), (uint)bits [2], (uint)bits [1], (uint)bits [0] };
 135                                 CustomAttributeBuilder cab = new CustomAttributeBuilder (TypeManager.decimal_constant_attribute_ctor, args);
 136                                 FieldBuilder.SetCustomAttribute (cab);
 137                         }
 138                         else{
 139                                 FieldBuilder.SetConstant (value.GetTypedValue ());
 140                         }
 141
 142                         base.Emit ();
 143                 }
 144
 145                 public static void Error_ExpressionMustBeConstant (Location loc, string e_name)
 146                 {
 147                         Report.Error (133, loc, "The expression being assigned to `{0}' must be constant", e_name);
 148                 }
 149
 150                 public static void Error_CyclicDeclaration (MemberCore mc)
 151                 {
 152                         Report.Error (110, mc.Location, "The evaluation of the constant value for `{0}' involves a circular definition",
 153                                 mc.GetSignatureForError ());
 154                 }
 155
 156                 public static void Error_ConstantCanBeInitializedWithNullOnly (Location loc, string name)
 157                 {
 158                         Report.Error (134, loc, "`{0}': the constant of reference type other than string can only be initialized with null",
 159                                 name);
 160                 }
 161
 162                 public static void Error_InvalidConstantType (Type t, Location loc)
 163                 {
 164                         Report.Error (283, loc, "The type `{0}' cannot be declared const", TypeManager.CSharpName (t));
 165                 }
 166
 167                 #region IConstant Members
 168
 169                 public bool ResolveValue ()
 170                 {
 171                         if (resolved)
 172                                 return value != null;
 173
 174                         SetMemberIsUsed ();
 175                         if (in_transit) {
 176                                 Error_CyclicDeclaration (this);
 177                                 // Suppress cyclic errors
 178                                 value = New.Constantify (MemberType);
 179                                 resolved = true;
 180                                 return false;
 181                         }
 182
 183                         in_transit = true;
 184                         // TODO: IResolveContext here
 185                         EmitContext ec = new EmitContext (
 186                                 this, Parent, Location, null, MemberType, ModFlags);
 187                         ec.InEnumContext = this is EnumMember;
 188                         value = DoResolveValue (ec);
 189                         in_transit = false;
 190                         resolved = true;
 191                         return value != null;
 192                 }
 193
 194                 protected virtual Constant DoResolveValue (EmitContext ec)
 195                 {
 196                         Constant value = initializer.ResolveAsConstant (ec, this);
 197                         if (value == null)
 198                                 return null;
 199
 200                         Constant c = value.ConvertImplicitly (MemberType);
 201                         if (c == null) {
 202                                 if (!MemberType.IsValueType && MemberType != TypeManager.string_type && !value.IsDefaultValue)
 203                                         Error_ConstantCanBeInitializedWithNullOnly (Location, GetSignatureForError ());
 204                                 else
 205                                         value.Error_ValueCannotBeConverted (null, Location, MemberType, false);
 206                         }
 207
 208                         return c;
 209                 }
 210
 211                 public virtual Constant CreateConstantReference (Location loc)
 212                 {
 213                         if (value == null)
 214                                 return null;
 215
 216                         return Constant.CreateConstant (value.Type, value.GetValue(), loc);
 217                 }
 218
 219                 #endregion
 220         }
 221
 222         public class ExternalConstant : IConstant
 223         {
 224                 FieldInfo fi;
 225                 object value;
 226
 227                 public ExternalConstant (FieldInfo fi)
 228                 {
 229                         this.fi = fi;
 230                 }
 231
 232                 private ExternalConstant (FieldInfo fi, object value):
 233                         this (fi)
 234                 {
 235                         this.value = value;
 236                 }
 237
 238                 //
 239                 // Decimal constants cannot be encoded in the constant blob, and thus are marked
 240                 // as IsInitOnly ('readonly' in C# parlance).  We get its value from the
 241                 // DecimalConstantAttribute metadata.
 242                 //
 243                 public static IConstant CreateDecimal (FieldInfo fi)
 244                 {
 245                         if (fi is FieldBuilder)
 246                                 return null;
 247
 248                         object[] attrs = fi.GetCustomAttributes (TypeManager.decimal_constant_attribute_type, false);
 249                         if (attrs.Length != 1)
 250                                 return null;
 251
 252                         IConstant ic = new ExternalConstant (fi,
 253                                 ((System.Runtime.CompilerServices.DecimalConstantAttribute) attrs [0]).Value);
 254
 255                         return ic;
 256                 }
 257
 258                 #region IConstant Members
 259
 260                 public void CheckObsoleteness (Location loc)
 261                 {
 262                         ObsoleteAttribute oa = AttributeTester.GetMemberObsoleteAttribute (fi);
 263                         if (oa == null) {
 264                                 return;
 265                         }
 266
 267                         AttributeTester.Report_ObsoleteMessage (oa, TypeManager.GetFullNameSignature (fi), loc);
 268                 }
 269
 270                 public bool ResolveValue ()
 271                 {
 272                         if (value != null)
 273                                 return true;
 274
 275                         value = fi.GetValue (fi);
 276                         return true;
 277                 }
 278
 279                 public Constant CreateConstantReference (Location loc)
 280                 {
 281                         return Constant.CreateConstant (fi.FieldType, value, loc);
 282                 }
 283
 284                 #endregion
 285         }
 286
 287 }