GroupedResultEnumerable.cs

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using System.Collections;
using System.Collections.Generic;
 
namespace System.Linq;
 
internal sealed class GroupedResultEnumerable<TSource, TKey, TElement, TResult> : IIListProvider<TResult>, IEnumerable<TResult>, IEnumerable
{
    private readonly IEnumerable<TSource> _source;
 
    private readonly Func<TSource, TKey> _keySelector;
 
    private readonly Func<TSource, TElement> _elementSelector;
 
    private readonly IEqualityComparer<TKey> _comparer;
 
    private readonly Func<TKey, IEnumerable<TElement>, TResult> _resultSelector;
 
    public TResult[] ToArray()
    {
        return Lookup<TKey, TElement>.Create(_source, _keySelector, _elementSelector, _comparer).ToArray(_resultSelector);
    }
 
    public List<TResult> ToList()
    {
        return Lookup<TKey, TElement>.Create(_source, _keySelector, _elementSelector, _comparer).ToList(_resultSelector);
    }
 
    public int GetCount(bool onlyIfCheap)
    {
        if (!onlyIfCheap)
        {
            return Lookup<TKey, TElement>.Create(_source, _keySelector, _elementSelector, _comparer).Count;
        }
        return -1;
    }
 
    public GroupedResultEnumerable(IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, Func<TKey, IEnumerable<TElement>, TResult> resultSelector, IEqualityComparer<TKey> comparer)
    {
        if (source == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
        }
        if (keySelector == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.keySelector);
        }
        if (elementSelector == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.elementSelector);
        }
        if (resultSelector == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.resultSelector);
        }
        _source = source;
        _keySelector = keySelector;
        _elementSelector = elementSelector;
        _comparer = comparer;
        _resultSelector = resultSelector;
    }
 
    public IEnumerator<TResult> GetEnumerator()
    {
        Lookup<TKey, TElement> lookup = Lookup<TKey, TElement>.Create(_source, _keySelector, _elementSelector, _comparer);
        return lookup.ApplyResultSelector(_resultSelector).GetEnumerator();
    }
 
    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}
internal sealed class GroupedResultEnumerable<TSource, TKey, TResult> : IIListProvider<TResult>, IEnumerable<TResult>, IEnumerable
{
    private readonly IEnumerable<TSource> _source;
 
    private readonly Func<TSource, TKey> _keySelector;
 
    private readonly IEqualityComparer<TKey> _comparer;
 
    private readonly Func<TKey, IEnumerable<TSource>, TResult> _resultSelector;
 
    public TResult[] ToArray()
    {
        return Lookup<TKey, TSource>.Create(_source, _keySelector, _comparer).ToArray(_resultSelector);
    }
 
    public List<TResult> ToList()
    {
        return Lookup<TKey, TSource>.Create(_source, _keySelector, _comparer).ToList(_resultSelector);
    }
 
    public int GetCount(bool onlyIfCheap)
    {
        if (!onlyIfCheap)
        {
            return Lookup<TKey, TSource>.Create(_source, _keySelector, _comparer).Count;
        }
        return -1;
    }
 
    public GroupedResultEnumerable(IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TKey, IEnumerable<TSource>, TResult> resultSelector, IEqualityComparer<TKey> comparer)
    {
        if (source == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
        }
        if (keySelector == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.keySelector);
        }
        if (resultSelector == null)
        {
            ThrowHelper.ThrowArgumentNullException(ExceptionArgument.resultSelector);
        }
        _source = source;
        _keySelector = keySelector;
        _resultSelector = resultSelector;
        _comparer = comparer;
    }
 
    public IEnumerator<TResult> GetEnumerator()
    {
        Lookup<TKey, TSource> lookup = Lookup<TKey, TSource>.Create(_source, _keySelector, _comparer);
        return lookup.ApplyResultSelector(_resultSelector).GetEnumerator();
    }
 
    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}