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