namespace HeuristicLab.Problems.ProgramSynthesis.Push.Expressions {
  using System;

  public abstract class StatefullExpression<T> : Expression {

    public readonly T State;
    private readonly Lazy<int> hashCode;

    protected StatefullExpression(T state) {
      this.State = state;
      this.hashCode = new Lazy<int>(this.CalcHashCode, true);
    }

    protected virtual int CalcHashCode() {
      return this.State.GetHashCode();
    }

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

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

      var other = (StatefullExpression<T>)obj;

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

    public override int GetHashCode() {
      return this.hashCode.Value;
    }
  }
}