Extension types cannot invoke static generic members.

[nathan130200]

I'm facing an issue while declaring some extension members.

Consider the function SHA1.HashData and MD5.HashData both of base HashAlgorithm i cannot dedclare an abstract hashing method that have this signature:

public static class Utilities
{
	extension<T>(T) where T : HashAlgorithm
	{
		public static string HashData(string data)
		{
			var buf = Encoding.UTF8.GetBytes(data);
			return Convert.ToBase64String(T.HashData(buf)); // <--- CS0704  T.HashData
		}
	}
}

CS0704: An inner type cannot be specified through a type parameter. Try using the desired type explicitly.

Its because all implementations of HashAlgorithm are not using have abstract interface feature?

But if i declare separated methods for both SHA1 and MD5 with same name HashData compiler show an error that same method with same name is already defined:

So the type i'm extending is not relevant to consider that extension memeber is for specific type?

So i must create a separated file to create for each extension methods for each existing hash algorithm (in this example)?

An work-around about this, i can map all existing subclasses of hash alg into a Dictionary<Type, Func<byte[], byte[]>> and invoke by calling typeof(T)

static readonly Dictionary<Type, Func<byte[], byte[]>> s_HashFunctions = new()
{
	[typeof(SHA1)] = SHA1.HashData,
	[typeof(MD5)] = MD5.HashData,
};

extension<T>(T) where T : HashAlgorithm
{
	public static string HashData(string data)
	{
		var buf = Encoding.UTF8.GetBytes(data);
		var hash = s_HashFunctions[typeof(T)](buf);
		return Convert.ToBase64String(hash);
	}
}

I think we need some kind of really abstract interface, that we should tell to compiler which methods we expect the type to implement, because the abstract interface members we actually need type implementing it.

public abtract interface IHashDataFunctions // abstract or new "trait" keyword
{
    public abstract static byte[] HashData(byte[] source); // static member

    public abstract const int HashSizeInBytes; // constant member

    public abstract bool TryComputeHash(ReadOnlySpan<byte> source, Span<byte> destination, out int bytesWritten); // instance member
}

...

public static byte[] HashData<T>(byte[] source) where T : IHashDataFunctions
{
  var minSize = T.HashSizeInBytes; // call consts

  return T.HashData(source); // call static, will no longer procudes CS0704

 // ...etc
}

[nathan130200]

N/a