Description
Problem:
Sometimes, it is useful to use arrays as keys in a map such as Dictionary. A motivating use case would be blockchain applications. Here, we often need to map a hash to some piece of data. For example, we might want to map a 32 byte block hash (byte[]) to block metadata.
Proposal:
There should be built-in equality comparers for sequences. By default, each element is default-compared. It should be possible to use a custom nested comparer.
I propose this API surface:
public static class EqualityComparer
{
public static IEqualityComparer<T[]> Array<T>(IEqualityComparer<T> elementComparer = null);
public static IEqualityComparer<Memory<T>> Memory<T>(IEqualityComparer<T> elementComparer = null);
public static IEqualityComparer<IEnumerable<T>> Sequence<T>(IEqualityComparer<T> elementComparer = null);
}
Example usage:
var dict = new Dictionary<byte[], BlockHeader>(EqualityComparer.Array<byte>());
These factory methods can internally pick an optimal comparer for the given arguments. For example, for arrays of primitive types, we can use memcmp-style algorithms internally. If a custom comparer is provided, an element-by-element comparison algorithm must be used. A cached instance can be used if no custom comparer is provided.
Possible extension: The same thing could be done for IComparer<T[]> (see #33873).