EmptySet.cs

using System;
using System.Collections.Generic;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Abstraction.Sets;
 
namespace Waher.Script.Objects.Sets
{
    public sealed class EmptySet : Set
    {
        private static readonly int hashCode = typeof(EmptySet).GetHashCode();
 
        public EmptySet()
        {
        }
 
        public static readonly EmptySet Instance = new EmptySet();
 
        public override bool Contains(IElement Element)
        {
            return false;
        }
 
        public override bool Equals(object obj)
        {
            return obj is EmptySet;
        }
 
        public override int GetHashCode()
        {
            return hashCode;
        }
 
        public override ICollection<IElement> ChildElements
        {
            get
            {
                return noElements;
            }
        }
 
        private static readonly IElement[] noElements = new IElement[0];
 
        public override int? Size
        {
            get { return 0; }
        }
 
        public override string ToString()
        {
            return "∅"; 
        }
 
    }
}