GroupJoinHashLookup.cs

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using System.Collections.Generic;
 
namespace System.Linq.Parallel;
 
internal abstract class GroupJoinHashLookup<THashKey, TElement, TBaseElement, TOrderKey> : HashJoinHashLookup<THashKey, IEnumerable<TElement>, TOrderKey>
{
    private readonly HashLookup<THashKey, TBaseElement> _base;
 
    protected abstract TOrderKey EmptyValueKey { get; }
 
    internal GroupJoinHashLookup(HashLookup<THashKey, TBaseElement> baseLookup)
    {
        _base = baseLookup;
    }
 
    public override bool TryGetValue(THashKey key, ref HashLookupValueList<IEnumerable<TElement>, TOrderKey> value)
    {
        Pair<IEnumerable<TElement>, TOrderKey> valueList = GetValueList(key);
        value = new HashLookupValueList<IEnumerable<TElement>, TOrderKey>(valueList.First, valueList.Second);
        return true;
    }
 
    private Pair<IEnumerable<TElement>, TOrderKey> GetValueList(THashKey key)
    {
        TBaseElement value = default(TBaseElement);
        if (_base.TryGetValue(key, ref value))
        {
            return CreateValuePair(value);
        }
        return new Pair<IEnumerable<TElement>, TOrderKey>(ParallelEnumerable.Empty<TElement>(), EmptyValueKey);
    }
 
    protected abstract Pair<IEnumerable<TElement>, TOrderKey> CreateValuePair(TBaseElement baseValue);
}