Grouping.cs

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using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
 
namespace System.Linq;
 
[DebuggerDisplay("Key = {Key}")]
[DebuggerTypeProxy(typeof(SystemLinq_GroupingDebugView<, >))]
public class Grouping<TKey, TElement> : IGrouping<TKey, TElement>, IEnumerable<TElement>, IEnumerable, IList<TElement>, ICollection<TElement>
{
    internal readonly TKey _key;
 
    internal readonly int _hashCode;
 
    internal TElement[] _elements;
 
    internal int _count;
 
    internal Grouping<TKey, TElement> _hashNext;
 
    internal Grouping<TKey, TElement> _next;
 
    public TKey Key => _key;
 
    int ICollection<TElement>.Count => _count;
 
    bool ICollection<TElement>.IsReadOnly => true;
 
    TElement IList<TElement>.this[int index]
    {
        get
        {
            if (index < 0 || index >= _count)
            {
                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index);
            }
            return _elements[index];
        }
        set
        {
            ThrowHelper.ThrowNotSupportedException();
        }
    }
 
    internal Grouping(TKey key, int hashCode)
    {
        _key = key;
        _hashCode = hashCode;
        _elements = new TElement[1];
    }
 
    internal void Add(TElement element)
    {
        if (_elements.Length == _count)
        {
            Array.Resize(ref _elements, checked(_count * 2));
        }
        _elements[_count] = element;
        _count++;
    }
 
    internal void Trim()
    {
        if (_elements.Length != _count)
        {
            Array.Resize(ref _elements, _count);
        }
    }
 
    public IEnumerator<TElement> GetEnumerator()
    {
        for (int i = 0; i < _count; i++)
        {
            yield return _elements[i];
        }
    }
 
    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
 
    void ICollection<TElement>.Add(TElement item)
    {
        ThrowHelper.ThrowNotSupportedException();
    }
 
    void ICollection<TElement>.Clear()
    {
        ThrowHelper.ThrowNotSupportedException();
    }
 
    bool ICollection<TElement>.Contains(TElement item)
    {
        return Array.IndexOf(_elements, item, 0, _count) >= 0;
    }
 
    void ICollection<TElement>.CopyTo(TElement[] array, int arrayIndex)
    {
        Array.Copy(_elements, 0, array, arrayIndex, _count);
    }
 
    bool ICollection<TElement>.Remove(TElement item)
    {
        ThrowHelper.ThrowNotSupportedException();
        return false;
    }
 
    int IList<TElement>.IndexOf(TElement item)
    {
        return Array.IndexOf(_elements, item, 0, _count);
    }
 
    void IList<TElement>.Insert(int index, TElement item)
    {
        ThrowHelper.ThrowNotSupportedException();
    }
 
    void IList<TElement>.RemoveAt(int index)
    {
        ThrowHelper.ThrowNotSupportedException();
    }
}