CachingComparerWithChild.cs

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using System.Collections.Generic;
 
namespace System.Linq;
 
internal sealed class CachingComparerWithChild<TElement, TKey> : CachingComparer<TElement, TKey>
{
    private readonly CachingComparer<TElement> _child;
 
    public CachingComparerWithChild(Func<TElement, TKey> keySelector, IComparer<TKey> comparer, bool descending, CachingComparer<TElement> child)
        : base(keySelector, comparer, descending)
    {
        _child = child;
    }
 
    internal override int Compare(TElement element, bool cacheLower)
    {
        TKey val = _keySelector(element);
        int num = (_descending ? _comparer.Compare(_lastKey, val) : _comparer.Compare(val, _lastKey));
        if (num == 0)
        {
            return _child.Compare(element, cacheLower);
        }
        if (cacheLower == num < 0)
        {
            _lastKey = val;
            _child.SetElement(element);
        }
        return num;
    }
 
    internal override void SetElement(TElement element)
    {
        base.SetElement(element);
        _child.SetElement(element);
    }
}