System.Collections.Immutable by Microsoft

<PackageReference Include="System.Collections.Immutable" Version="8.0.0-preview.1.23110.8" />

.NET API 249,008 bytes

FrozenSet

public static class FrozenSet

public static FrozenSet<T> ToFrozenSet<T>(this IEnumerable<T> source, IEqualityComparer<T> comparer = null)

public static FrozenSet<T> ToFrozenSet<T>(this IEnumerable<T> source, bool optimizeForReading)

public static FrozenSet<T> ToFrozenSet<T>(this IEnumerable<T> source, IEqualityComparer<T> comparer, bool optimizeForReading)