namespace System.Collections.Frozen { public static class FrozenDictionary { public static FrozenDictionary<TKey, TValue> Create<TKey, [System.Runtime.CompilerServices.Nullable(2)] TValue>(ReadOnlySpan<KeyValuePair<TKey, TValue>> source); public static FrozenDictionary<TKey, TValue> Create<TKey, [System.Runtime.CompilerServices.Nullable(2)] TValue>(IEqualityComparer<TKey> comparer, ReadOnlySpan<KeyValuePair<TKey, TValue>> source); public static FrozenDictionary<TKey, TValue> ToFrozenDictionary<TKey, [System.Runtime.CompilerServices.Nullable(2)] TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> source, IEqualityComparer<TKey> comparer = null); public static FrozenDictionary<TKey, TSource> ToFrozenDictionary<[System.Runtime.CompilerServices.Nullable(2)] TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer = null); public static FrozenDictionary<TKey, TElement> ToFrozenDictionary<[System.Runtime.CompilerServices.Nullable(2)] TSource, TKey, [System.Runtime.CompilerServices.Nullable(2)] TElement>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, IEqualityComparer<TKey> comparer = null); } }