Please add interface IReadOnlySet and make HashSet, SortedSet implement it #2293
Description
Original
Since IReadOnlyList was added the parity between sets and lists has declined. It would be great to re-establish it.
Using it would be an implementation-agnostic way of saying: "here is this read-only collection where items are unique".
Clearly it's needed by many people:
SQL Server: https://msdn.microsoft.com/en-us/library/gg503096.aspx
Roslyn: https://github.com/dotnet/roslyn/blob/master/src/Compilers/Core/Portable/InternalUtilities/IReadOnlySet.cs
Some Guy In Comments: http://blogs.msdn.com/b/bclteam/archive/2013/03/06/update-to-immutable-collections.aspx
I found this discussion when working on a real world problem where I wanted to use the key collection of a dictionary for read only set operations. In order to support that case here's the API I propose.
Edit
Rationale
Proposed API
namespace System.Collections.Generic {
+ public interface IReadOnlySet<out T> : IReadOnlyCollection<T>, IEnumerable, IEnumerable<T> {
+ bool Contains(T value);
+ bool IsProperSubsetOf(IEnumerable<T> other);
+ bool IsProperSupersetOf(IEnumerable<T> other);
+ bool IsSubsetOf(IEnumerable<T> other);
+ bool IsSupersetOf(IEnumerable<T> other);
+ bool Overlaps(IEnumerable<T> other);
+ bool SetEquals(IEnumerable<T> other);
+ }
- public class HashSet<T> : ICollection<T>, IDeserializationCallback, IEnumerable, IEnumerable<T>, IReadOnlyCollection<T>, ISerializable, ISet<T> {
+ public class HashSet<T> : ICollection<T>, IDeserializationCallback, IEnumerable, IEnumerable<T>, IReadOnlyCollection<T>, ISerializable, ISet<T>, IReadOnlySet<T> {
}
- public class SortedSet<T> : ICollection, ICollection<T>, IDeserializationCallback, IEnumerable, IEnumerable<T>, IReadOnlyCollection<T>, ISerializable, ISet<T> {
+ public class SortedSet<T> : ICollection, ICollection<T>, IDeserializationCallback, IEnumerable, IEnumerable<T>, IReadOnlyCollection<T>, ISerializable, ISet<T>, IReadOnlySet<T> {
}
+ public class ReadOnlySet<T> : ICollection<T>, IEnumerable, IEnumerable<T>, IReadOnlyCollection<T>, IReadOnlySet<T>, ISet<T> {
+ public int Count { get; }
+ public ReadOnlySet(ISet<T> set);
+ public bool Contains(T value);
+ public bool IsProperSubsetOf(IEnumerable<T> other);
+ public bool IsProperSupersetOf(IEnumerable<T> other);
+ public bool IsSubsetOf(IEnumerable<T> other);
+ public bool IsSupersetOf(IEnumerable<T> other);
+ public bool Overlaps(IEnumerable<T> other);
+ public bool SetEquals(IEnumerable<T> other);
+ }
public class Dictionary<TKey, TValue> {
- public sealed class KeyCollection : ICollection, ICollection<TKey>, IEnumerable, IEnumerable<TKey>, IReadOnlyCollection<TKey> {
+ public sealed class KeyCollection : ICollection, ICollection<TKey>, IEnumerable, IEnumerable<TKey>, IReadOnlyCollection<TKey>, IReadOnlySet<TKey> {
+ public bool IsProperSubsetOf(IEnumerable<TKey> other);
+ public bool IsProperSupersetOf(IEnumerable<TKey> other);
+ public bool IsSubsetOf(IEnumerable<TKey> other);
+ public bool IsSupersetOf(IEnumerable<TKey> other);
+ public bool Overlaps(IEnumerable<TKey> other);
+ public bool SetEquals(IEnumerable<TKey> other);
}
}
}Open Questions
- Is adding these methods to
Dictionary<TKey, TValue>.KeyCollectionacceptable given the code size cost for a commonly instantiated generic type? See here. - Should
IReadOnlySet<T>be implemented in otherDictionaryKeyCollections such asSortedDictionaryorImmutableDictionary?
Updates
- Removed
TryGetValueas it's not inISet<T>and as such would prevent potentially ever rebasingISet<T>to implementIReadOnlySet<T>. - Added
ReadOnlySet<T>class which is similar toReadOnlyCollection<T>.