NullValue.cs

using System;
using Waher.Runtime.Inventory;
 
namespace Waher.Content.Semantic.Model.Literals
{
    public class NullValue : SemanticLiteral
    {
        internal static readonly NullValue Instance = new NullValue();
 
        public NullValue()
            : base(null, string.Empty)
        {
        }
 
        public override object AssociatedObjectValue => null;
 
        public override string StringType => string.Empty;
 
        public override int CompareTo(object obj)
        {
            return obj is NullValue ? 0 : -1;
        }
 
        public override string ToString()
        {
            return string.Empty;
        }
 
        public override bool Equals(object obj)
        {
            return obj.GetType() == typeof(NullValue);
        }
 
        public override int GetHashCode()
        {
            return this.GetType().GetHashCode();
        }
 
        public override Grade Supports(string DataType)
        {
            return Grade.NotAtAll;
        }
 
        public override Grade Supports(Type ValueType)
        {
            return Grade.NotAtAll;
        }
 
        public override ISemanticLiteral Parse(string Value, string DataType, string Language)
        {
            if (Value is null)
                return new NullValue();
            else
                return new CustomLiteral(Value, DataType, Language);
        }
 
        public override ISemanticLiteral Encapsulate(object Value)
        {
            if (Value is null)
                return new NullValue();
            else if (SemanticElements.Encapsulate(Value) is ISemanticLiteral Literal)
                return Literal;
            else
                throw new ArgumentException("Not a literal.", nameof(Value));
        }
    }
}