mcs/class/referencesource/System.Data.Entity/System/Data/Common/Utils/Boolean/Literal.cs

   1 //---------------------------------------------------------------------
   2 // <copyright file="Literal.cs" company="Microsoft">
   3 //      Copyright (c) Microsoft Corporation.  All rights reserved.
   4 // </copyright>
   5 //
   6 // @owner Microsoft
   7 // @backupOwner Microsoft
   8 //---------------------------------------------------------------------
   9
  10 using System;
  11 using System.Collections.Generic;
  12 using System.Text;
  13 using System.Globalization;
  14 using System.Collections.ObjectModel;
  15 using System.Diagnostics;
  16
  17 namespace System.Data.Common.Utils.Boolean
  18 {
  19     /// <summary>
  20     /// Represents a literal in a normal form expression of the form:
  21     ///
  22     ///         Term
  23     ///
  24     /// or
  25     ///
  26     ///         !Term
  27     /// </summary>
  28     /// <typeparam name="T_Identifier"></typeparam>
  29     internal sealed class Literal<T_Identifier> : NormalFormNode<T_Identifier>,
  30         IEquatable<Literal<T_Identifier>>
  31     {
  32         private readonly TermExpr<T_Identifier> _term;
  33         private readonly bool _isTermPositive;
  34
  35         /// <summary>
  36         /// Initialize a new literal.
  37         /// </summary>
  38         /// <param name="term">Term</param>
  39         /// <param name="isTermPositive">Sign of term</param>
  40         internal Literal(TermExpr<T_Identifier> term, bool isTermPositive)
  41             : base(isTermPositive ? (BoolExpr<T_Identifier>)term : (BoolExpr<T_Identifier>)new NotExpr<T_Identifier>(term))
  42         {
  43             Debug.Assert(null != term);
  44             _term = term;
  45             _isTermPositive = isTermPositive;
  46         }
  47
  48         /// <summary>
  49         /// Gets literal term.
  50         /// </summary>
  51         internal TermExpr<T_Identifier> Term
  52         {
  53             get { return _term; }
  54         }
  55
  56         /// <summary>
  57         /// Gets sign of term.
  58         /// </summary>
  59         internal bool IsTermPositive
  60         {
  61             get { return _isTermPositive; }
  62         }
  63
  64         /// <summary>
  65         /// Creates a negated version of this literal.
  66         /// </summary>
  67         /// <returns>!this</returns>
  68         internal Literal<T_Identifier> MakeNegated()
  69         {
  70             return IdentifierService<T_Identifier>.Instance.NegateLiteral(this);
  71         }
  72
  73         public override string ToString()
  74         {
  75             return StringUtil.FormatInvariant("{0}{1}",
  76                 _isTermPositive ? String.Empty : "!",
  77                 _term);
  78         }
  79
  80         public override bool Equals(object obj)
  81         {
  82             Debug.Fail("use typed Equals");
  83             return Equals(obj as Literal<T_Identifier>);
  84         }
  85
  86         public bool Equals(Literal<T_Identifier> other)
  87         {
  88             return null != other &&
  89                 other._isTermPositive == _isTermPositive &&
  90                 other._term.Equals(_term);
  91         }
  92
  93         public override int GetHashCode()
  94         {
  95             return _term.GetHashCode();
  96         }
  97     }
  98 }