[API Proposal]: Non-Generic base type

[michaelgsharp]

Background and motivation

We currently do not have a non-generic base type for Tensor. This is fine, but there are many times you need info about the Tensor (its rank, lengths of dimenions, etc) and you can get this info without needing to know or care about the generic type itself. We need to add a base type that will better facilitate this.

We can evaluate whether we need to add more methods, maybe involving boxing, as time goes on.

API Proposal

namespace System.Numerics.Tensors;

// All of these existed in higher types. Just creating a new base type and moving these down.
public interface ITensor
{
    /// <summary>
    /// Gets a value that indicates whether the collection is currently empty.
    /// </summary>
    bool IsEmpty { get; }

    /// <summary>
    /// Gets a value that indicates whether the underlying buffer is pinned.
    /// </summary>
    bool IsPinned { get; }

    /// <summary>
    /// Gets the number of elements in the tensor.
    /// </summary>
    nint FlattenedLength { get; }

    /// <summary>
    /// Gets the number of dimensions in the tensor.
    /// </summary>
    int Rank { get; }

    /// <summary>
    /// Gets the length of each dimension in the tensor.
    /// </summary>
    [UnscopedRef]
    ReadOnlySpan<nint> Lengths { get; }

    /// <summary>
    /// Gets the stride of each dimension in the tensor.
    /// </summary>
    [UnscopedRef]
    ReadOnlySpan<nint> Strides { get; }
}

API Usage

public void DoStuffWithNonGenericTensor(ITensor tensor);

Tensor<int> tensor = Tensor.Create<int>([1, 2, 3, 4], [2, 2]);

DoStuffWithNonGenericTensor(tensor);

Alternative Designs

Potentially have more methods for getting data involving boxing.

Risks

Low risk because it's a preview type, but because we are changing the class heirarchy there is more than none.

[michaelgsharp]

@tannergooding

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[tannergooding]

We can evaluate whether we need to add more methods, maybe involving boxing, as time goes on.

This notably needs to be decided up front, prior to shipping, as we cannot expose such APIs after we ship it as stable.

Such considerations should likely be part of this API proposal.