source: branches/2895_PushGP_GenealogyAnalysis/HeuristicLab.Problems.ProgramSynthesis/Push/Expressions/StatefulExpression.cs @ 15771

using System;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;

namespace HeuristicLab.Problems.ProgramSynthesis {
  [Serializable]
  [StorableClass]
  public abstract class StatefulExpression<T> : Expression, IPooledObject {
    [Storable]
    public T State { get; protected set; }
    [NonSerialized]
    private int? hashCode;
    [NonSerialized]
    private string stringRepresentation;

    protected StatefulExpression(T state) {
      State = state;
    }

    [StorableConstructor]
    protected StatefulExpression(bool deserializing) : base(deserializing) { }

    protected virtual int CalcHashCode() {
      var hash = 19 * 31 + GetType().FullName.GetHashCode();
      hash = hash * 31 + State.GetHashCode();

      return hash;
    }

    protected virtual string GetStringRepresentation() {
      return State.ToString();
    }

    public override string StringRepresentation {
      get {
        return stringRepresentation ?? (stringRepresentation = GetStringRepresentation());
      }
    }

    public override bool Equals(object obj) {
      if (ReferenceEquals(this, obj))
        return true;

      if (GetType() != obj.GetType())
        return false;

      var other = (StatefulExpression<T>)obj;

      return ReferenceEquals(State, other.State) ||
             GetHashCode() == other.GetHashCode();
    }

    public bool Equals(StatefulExpression<T> obj) {
      if (ReferenceEquals(this, obj))
        return true;

      if (GetType() != obj.GetType())
        return false;

      return ReferenceEquals(State, obj.State) ||
             GetHashCode() == obj.GetHashCode();
    }

    public override int GetHashCode() {
      if (hashCode == null) hashCode = CalcHashCode();
      return hashCode.Value;
    }

    public void Reset() {
      State = default(T);
    }
  }
}