//---------------------------------------------------------------------------
//
// <copyright file="EmptyEnumerator" company="Microsoft">
//    Copyright (C) Microsoft Corporation.  All rights reserved.
// </copyright>
// 
//
// Description: Empty enumerator
//
// History:  
//  02/26/2004 : JeffBog stole from ItemsView (and stole comments from UIAutomation)
//
//---------------------------------------------------------------------------
using System;
using System.Collections;
 
namespace MS.Internal.Controls
{
    /// <summary>
    /// Returns an Enumerator that enumerates over nothing.
    /// </summary>
    internal class EmptyEnumerator: IEnumerator
    {
        // singleton class, private ctor
        private EmptyEnumerator()
        {
        }
 
        /// <summary>
        /// Read-Only instance of an Empty Enumerator.
        /// </summary>
        public static IEnumerator Instance
        {
            get
            {
                if (_instance == null)
                {
                    _instance = new EmptyEnumerator();
                }
                return _instance;
            }
        }
 
        /// <summary>
        /// Does nothing.
        /// </summary>
        public void Reset() { }
 
        /// <summary>
        /// Returns false.
        /// </summary>
        /// <returns>false</returns>
        public bool MoveNext() { return false; }
 
 
#pragma warning disable 1634, 1691  // about to use PreSharp message numbers - unknown to C#
 
        /// <summary>
        /// Returns null.
        /// </summary>
        public object Current { 
            get 
            { 
                #pragma warning disable 6503 // "Property get methods should not throw exceptions."
 
                throw new InvalidOperationException(); 
 
                #pragma warning restore 6503
            }
        }
#pragma warning restore 1634, 1691
 
        private static IEnumerator _instance;
    }
}