mcs/class/referencesource/System.Xml/System/Xml/XPath/Internal/CacheAxisQuery.cs


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//------------------------------------------------------------------------------
// <copyright file="CacheAxisQuery.cs" company="Microsoft">
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>                                                                
// <owner current="true" primary="true">[....]</owner>
//------------------------------------------------------------------------------

namespace MS.Internal.Xml.XPath {
    using System;
    using System.Xml;
    using System.Xml.XPath;
    using System.Diagnostics;
    using System.Collections.Generic;

    internal abstract class CacheAxisQuery : BaseAxisQuery {
        // int count; -- we reusing it here
        protected List<XPathNavigator> outputBuffer;

        public CacheAxisQuery(Query qyInput, string name, string prefix, XPathNodeType typeTest) : base(qyInput, name, prefix, typeTest)  {
            this.outputBuffer = new List<XPathNavigator>();
            this.count = 0;
        }
        protected CacheAxisQuery(CacheAxisQuery other) : base(other) { 
            this.outputBuffer = new List<XPathNavigator>(other.outputBuffer);
            this.count = other.count;
        }

        public override void Reset() {
            this.count = 0;
        }

        public override object Evaluate(XPathNodeIterator context) {
            base.Evaluate(context);
            outputBuffer.Clear();
            return this;
        }

        public override XPathNavigator Advance() {
            Debug.Assert(0 <= count && count <= outputBuffer.Count);
            if (count < outputBuffer.Count) {
                return outputBuffer[count++];
            }
            return null;
        }
        
        public override XPathNavigator Current { 
            get {
                Debug.Assert(0 <= count && count <= outputBuffer.Count);
                if (count == 0) {
                    return null;
                }
                return outputBuffer[count - 1];
            } 
        }

        public override int CurrentPosition   { get { return count; } }
        public override int Count             { get { return outputBuffer.Count; } }
        public override QueryProps Properties { get { return QueryProps.Merge | QueryProps.Cached | QueryProps.Position | QueryProps.Count; } }
    }
}