This repository was archived by the owner on Aug 2, 2023. It is now read-only.
This repository was archived by the owner on Aug 2, 2023. It is now read-only.
Add a StringKeyedDictionary<T> type #2438
Description
Motivation
As part of the #2406 initiative I would like a StringKeyedDictionary<T> type added in order to allow using a ReadOnlySpan<char> value for dictionary lookups without having to allocate a string.
Proposed API
namespace System.Collections.Specialized {
+ public class StringKeyedDictionary<T> : Dictionary<string, T> {
+ public StringKeyedDictionary();
+ public StringKeyedDictionary(IStringEqualityComparer comparer);
+ public StringKeyedDictionary(int capacity);
+ public StringKeyedDictionary(int capacity, IStringEqualityComparer comparer);
+ public StringKeyedDictionary(IDictionary<string, T> dictionary);
+ public StringKeyedDictionary(IDictionary<string, T> dictionary, IStringEqualityComparer comparer);
+ public StringKeyedDictionary(IEnumerable<KeyValuePair<string, T>> collection);
+ public StringKeyedDictionary(IEnumerable<KeyValuePair<string, T>> collection, IStringEqualityComparer comparer);
+ public new IStringEqualityComparer Comparer { get; }
+ public T this[ReadOnlySpan<char> key] { get; }
+ public bool ContainsKey(ReadOnlySpan<char> key);
+ public bool Remove(ReadOnlySpan<char> key);
+ public bool TryGetValue(ReadOnlySpan<char> key, out T value);
+ }
+ public interface IStringEqualityComparer : IEqualityComparer<string> {
+ bool Equals(ReadOnlySpan<char> x, ReadOnlySpan<char> y);
+ int GetHashCode(ReadOnlySpan<char> obj);
+ }
}
namespace System {
- public abstract class StringComparer : IComparer<string>, IEqualityComparer<string>, IComparer, IEqualityComparer {
+ public abstract class StringComparer : IComparer<string>, IEqualityComparer<string>, IComparer, IEqualityComparer, IStringEqualityComparer {
+ public virtual bool Equals(ReadOnlySpan<char> x, ReadOnlySpan<char> y);
+ public virtual int GetHashCode(ReadOnlySpan<char> obj);
}
public sealed class CultureAwareComparer : StringComparer {
+ public override bool Equals(ReadOnlySpan<char> x, ReadOnlySpan<char> y);
+ public override int GetHashCode(ReadOnlySpan<char> obj);
}
public class OrdinalComparer : StringComparer {
+ public override bool Equals(ReadOnlySpan<char> x, ReadOnlySpan<char> y);
+ public override int GetHashCode(ReadOnlySpan<char> obj);
}
}Implementation Details
- The default implementation of the new virtual methods on
StringComparerwould convert the span to a string and use the string methods instead. - Internal details of
Dictionary<TKey, TValue>would be needed to implement theReadOnlySpan<char>overloads. - A
nullcomparer passed to the constructor would default toStringComparer.Ordinal. - Would need to be implemented in corefx to access internal
Dictionary<TKey, TValue>details as well as updateStringComparer.
Possible Addition
While not specifically needed for this request an IStringComparer interface should probably be added as well like so since we're updating StringComparer. It could then be used in a specialized StringKeyedSortedDictionary or StringSortedSet.
namespace System.Collections.Specialized {
+ public interface IStringComparer : IComparer<string> {
+ int Compare(ReadOnlySpan<char> x, ReadOnlySpan<char> y);
+ }
}
namespace System {
- public abstract class StringComparer : IComparer, IEqualityComparer, IComparer<string>, IEqualityComparer<string>, IStringEqualityComparer {
+ public abstract class StringComparer : IComparer, IEqualityComparer, IComparer<string>, IEqualityComparer<string>, IStringEqualityComparer, IStringComparer {
+ public virtual int Compare(ReadOnlySpan<char> x, ReadOnlySpan<char> y);
}
public sealed class CultureAwareComparer : StringComparer {
+ public override int Compare(ReadOnlySpan<char> x, ReadOnlySpan<char> y);
}
public class OrdinalComparer : StringComparer {
+ public override int Compare(ReadOnlySpan<char> x, ReadOnlySpan<char> y);
}
}Open Questions
- Should the additional
IStringComparerinterface also be implemented?
Updates
- Switched to proposing implementation that derives from
Dictionary<string, T>due to the massive code duplication of re-implementingDictionary<TKey, TValue>'s logic.