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