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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Diagnostics;
using System.Linq;
namespace System.Collections.Frozen
{
/// <summary>Provides a frozen set to use when the item is a value type, the default comparer is used, and the item count is small.</summary>
/// <remarks>
/// While not constrained in this manner, the <typeparamref name="T"/> must be an <see cref="IComparable{T}"/>.
/// This implementation is only used for a set of types that have a known-good <see cref="IComparable{T}"/> implementation; it's not
/// used for an <see cref="IComparable{T}"/> as we can't know for sure whether it's valid, e.g. if the T is a ValueTuple`2, it itself
/// is comparable, but its items might not be such that trying to compare it will result in exception.
/// </remarks>
internal sealed class SmallValueTypeComparableFrozenSet<T> : FrozenSetInternalBase<T, SmallValueTypeComparableFrozenSet<T>.GSW>
{
private readonly T[] _items;
private readonly T _max;
internal SmallValueTypeComparableFrozenSet(HashSet<T> source) : base(EqualityComparer<T>.Default)
{
Debug.Assert(default(T) is IComparable<T>);
Debug.Assert(default(T) is not null);
Debug.Assert(typeof(T).IsValueType);
Debug.Assert(source.Count != 0);
Debug.Assert(ReferenceEquals(source.Comparer, EqualityComparer<T>.Default));
_items = source.ToArray();
Array.Sort(_items);
_max = _items[_items.Length - 1];
}
private protected override T[] ItemsCore => _items;
private protected override Enumerator GetEnumeratorCore() => new Enumerator(_items);
private protected override int CountCore => _items.Length;
private protected override int FindItemIndex(T item)
{
if (Comparer<T>.Default.Compare(item, _max) <= 0)
{
T[] items = _items;
for (int i = 0; i < items.Length; i++)
{
int c = Comparer<T>.Default.Compare(item, items[i]);
if (c <= 0)
{
if (c == 0)
{
return i;
}
break;
}
}
}
return -1;
}
internal struct GSW : IGenericSpecializedWrapper
{
private SmallValueTypeComparableFrozenSet<T> _set;
public void Store(FrozenSet<T> set) => _set = (SmallValueTypeComparableFrozenSet<T>)set;
public int Count => _set.Count;
public IEqualityComparer<T> Comparer => _set.Comparer;
public int FindItemIndex(T item) => _set.FindItemIndex(item);
public Enumerator GetEnumerator() => _set.GetEnumerator();
}
}
}
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