XPathEvaluator.cs

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using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Xml.Linq;
 
namespace System.Xml.XPath;
 
[StructLayout(LayoutKind.Sequential, Size = 1)]
internal readonly struct XPathEvaluator
{
    public object Evaluate<T>(XNode node, string expression, IXmlNamespaceResolver resolver) where T : class
    {
        XPathNavigator xPathNavigator = node.CreateNavigator();
        object obj = xPathNavigator.Evaluate(expression, resolver);
        if (obj is XPathNodeIterator result)
        {
            return EvaluateIterator<T>(result);
        }
        if (!(obj is T))
        {
            throw new InvalidOperationException(System.SR.Format(System.SR.InvalidOperation_UnexpectedEvaluation, obj.GetType()));
        }
        return (T)obj;
    }
 
    private IEnumerable<T> EvaluateIterator<T>(XPathNodeIterator result)
    {
        foreach (XPathNavigator item in result)
        {
            object r = item.UnderlyingObject;
            if (!(r is T))
            {
                throw new InvalidOperationException(System.SR.Format(System.SR.InvalidOperation_UnexpectedEvaluation, r.GetType()));
            }
            yield return (T)r;
            XText t = r as XText;
            if (t == null || t.GetParent() == null)
            {
                continue;
            }
            do
            {
                t = t.NextNode as XText;
                if (t == null)
                {
                    break;
                }
                yield return (T)(object)t;
            }
            while (t != t.GetParent().LastNode);
        }
    }
}