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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.Diagnostics;
using System.Linq;
using System.Runtime.CompilerServices;
namespace System.Collections.Frozen
{
/// <summary>Provides a frozen dictionary to use when the key 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="TKey"/> 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 TKey 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 SmallValueTypeComparableFrozenDictionary<TKey, TValue> : FrozenDictionary<TKey, TValue>
where TKey : notnull
{
private readonly TKey[] _keys;
private readonly TValue[] _values;
private readonly TKey _max;
internal SmallValueTypeComparableFrozenDictionary(Dictionary<TKey, TValue> source) : base(EqualityComparer<TKey>.Default)
{
Debug.Assert(default(TKey) is IComparable<TKey>);
Debug.Assert(default(TKey) is not null);
Debug.Assert(typeof(TKey).IsValueType);
Debug.Assert(source.Count != 0);
Debug.Assert(ReferenceEquals(source.Comparer, EqualityComparer<TKey>.Default));
_keys = source.Keys.ToArray();
_values = source.Values.ToArray();
Array.Sort(_keys, _values);
_max = _keys[_keys.Length - 1];
}
private protected override TKey[] KeysCore => _keys;
private protected override TValue[] ValuesCore => _values;
private protected override Enumerator GetEnumeratorCore() => new Enumerator(_keys, _values);
private protected override int CountCore => _keys.Length;
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private protected override ref readonly TValue GetValueRefOrNullRefCore(TKey key)
{
if (Comparer<TKey>.Default.Compare(key, _max) <= 0)
{
TKey[] keys = _keys;
for (int i = 0; i < keys.Length; i++)
{
int c = Comparer<TKey>.Default.Compare(key, keys[i]);
if (c <= 0)
{
if (c == 0)
{
return ref _values[i];
}
break;
}
}
}
return ref Unsafe.NullRef<TValue>();
}
}
}
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