mcs/class/Mono.CodeContracts/Mono.CodeContracts.Static.Analysis.ExpressionAnalysis.Expressions/NullExpr.cs

   1 //
   2 // NullExpr.cs
   3 //
   4 // Authors:
   5 //      Alexander Chebaturkin (chebaturkin@gmail.com)
   6 //
   7 // Copyright (C) 2011 Alexander Chebaturkin
   8 //
   9 // Permission is hereby granted, free of charge, to any person obtaining
  10 // a copy of this software and associated documentation files (the
  11 // "Software"), to deal in the Software without restriction, including
  12 // without limitation the rights to use, copy, modify, merge, publish,
  13 // distribute, sublicense, and/or sell copies of the Software, and to
  14 // permit persons to whom the Software is furnished to do so, subject to
  15 // the following conditions:
  16 //
  17 // The above copyright notice and this permission notice shall be
  18 // included in all copies or substantial portions of the Software.
  19 //
  20 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  21 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  22 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  23 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  24 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  25 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  26 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  27 //
  28
  29 using System;
  30 using System.Collections.Generic;
  31 using Mono.CodeContracts.Static.ControlFlow;
  32 using Mono.CodeContracts.Static.DataStructures;
  33
  34 namespace Mono.CodeContracts.Static.Analysis.ExpressionAnalysis.Expressions {
  35         sealed class NullExpr<TSymbolicValue> : Expr<TSymbolicValue> where TSymbolicValue : IEquatable<TSymbolicValue> {
  36                 public static readonly Expr<TSymbolicValue> Instance = new NullExpr<TSymbolicValue> ();
  37
  38                 private NullExpr ()
  39                 {
  40                 }
  41
  42                 #region Overrides of Expression
  43                 public override IEnumerable<TSymbolicValue> Variables
  44                 {
  45                         get { yield break; }
  46                 }
  47
  48                 public override Result Decode<Data, Result, Visitor> (APC pc, TSymbolicValue dest, Visitor visitor, Data data)
  49                 {
  50                         return visitor.LoadNull (pc, dest, data);
  51                 }
  52
  53                 public override Expr<TSymbolicValue> Substitute (IImmutableMap<TSymbolicValue, Sequence<TSymbolicValue>> substitutions)
  54                 {
  55                         return this;
  56                 }
  57
  58                 public override bool IsContained (IImmutableSet<TSymbolicValue> candidates)
  59                 {
  60                         return false;
  61                 }
  62
  63                 public override bool Contains (TSymbolicValue symbol)
  64                 {
  65                         return false;
  66                 }
  67
  68                 public override string ToString ()
  69                 {
  70                         return "Null()";
  71                 }
  72
  73                 public override bool Equals (Expr<TSymbolicValue> other)
  74                 {
  75                         return other == this;
  76                 }
  77                 #endregion
  78         }
  79 }