Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/System.Xml/System/Xml/XPath/XPathNodeIterator.cs

@@ -0,0 +1,114 @@
+//------------------------------------------------------------------------------
+// <copyright file="XPathNodeIterator.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+// <owner current="true" primary="true">[....]</owner>
+//------------------------------------------------------------------------------
+
+using System.Collections;
+using System.Diagnostics;
+using System.Text;
+
+namespace System.Xml.XPath {
+
+    [DebuggerDisplay("Position={CurrentPosition}, Current={debuggerDisplayProxy}")]
+    public abstract class XPathNodeIterator : ICloneable, IEnumerable {
+        internal int count = -1;
+
+        object ICloneable.Clone() { return this.Clone(); }
+
+        public abstract XPathNodeIterator Clone();
+        public abstract bool MoveNext();
+        public abstract XPathNavigator Current { get; }
+        public abstract int CurrentPosition { get; }
+        public virtual int Count {
+            get {
+                if (count == -1) {
+                    XPathNodeIterator clone = this.Clone();
+                    while(clone.MoveNext()) ;
+                    count = clone.CurrentPosition;
+                }
+                return count;
+            }
+        }
+        public virtual IEnumerator GetEnumerator() {
+            return new Enumerator(this);
+        }
+
+        private object debuggerDisplayProxy { get { return Current == null ? null : (object)new XPathNavigator.DebuggerDisplayProxy(Current); } }
+
+        /// <summary>
+        /// Implementation of a resetable enumerator that is linked to the XPathNodeIterator used to create it.
+        /// </summary>
+        private class Enumerator : IEnumerator {
+            private XPathNodeIterator original;     // Keep original XPathNodeIterator in case Reset() is called
+            private XPathNodeIterator current;
+            private bool iterationStarted;
+
+            public Enumerator(XPathNodeIterator original) {
+                this.original = original.Clone();
+            }
+
+            public virtual object Current {
+                get {
+                    // 1. Do not reuse the XPathNavigator, as we do in XPathNodeIterator
+                    // 2. Throw exception if current position is before first node or after the last node
+                    if (this.iterationStarted) {
+                        // Current is null if iterator is positioned after the last node
+                        if (this.current == null)
+                            throw new InvalidOperationException(Res.GetString(Res.Sch_EnumFinished, string.Empty));
+
+                        return this.current.Current.Clone();
+                    }
+
+                    // User must call MoveNext before accessing Current property
+                    throw new InvalidOperationException(Res.GetString(Res.Sch_EnumNotStarted, string.Empty));
+                }
+            }
+
+            public virtual bool MoveNext() {
+                // Delegate to XPathNodeIterator
+                if (!this.iterationStarted) {
+                    // Reset iteration to original position
+                    this.current = this.original.Clone();
+                    this.iterationStarted = true;
+                }
+
+                if (this.current == null || !this.current.MoveNext()) {
+                    // Iteration complete
+                    this.current = null;
+                    return false;
+                }
+                return true;
+            }
+
+            public virtual void Reset() {
+                this.iterationStarted = false;
+            }
+        }
+
+        private struct DebuggerDisplayProxy {
+            private XPathNodeIterator nodeIterator;
+
+            public DebuggerDisplayProxy(XPathNodeIterator nodeIterator) {
+                this.nodeIterator = nodeIterator;
+            }
+
+            public override string ToString() {
+                // Position={CurrentPosition}, Current={Current == null ? null : (object) new XPathNavigator.DebuggerDisplayProxy(Current)}
+                StringBuilder sb = new StringBuilder();
+                sb.Append("Position=");
+                sb.Append(nodeIterator.CurrentPosition);
+                sb.Append(", Current=");
+                if (nodeIterator.Current == null) {
+                    sb.Append("null");
+                } else {
+                    sb.Append('{');
+                    sb.Append(new XPathNavigator.DebuggerDisplayProxy(nodeIterator.Current).ToString());
+                    sb.Append('}');
+                }
+                return sb.ToString();
+            }
+        }
+    }
+}