Evaluate the opportunity to replace gonum.DirectedWeightedBuilder in the top level Model

[owulveryck]

The Model is an encapsulation of gonum.DirectedWeightedBuilder's interface.

This gives some great flexibility for implementing a backend.
For example, you can create a very simple backend (see the example in "simple") simply to display the graph in case you do not need actually to compute the result.
For example, I am using this to create a dot representation of the onnx graph.

If the backend needs more feature, the backend can fulfill this interface, and the corresponding method is applied at runtime :

type OperationCarrier interface {
        ApplyOperation(Operation, graph.Node) error
}

The problem is that a type inference is made at runtime and this process is slow.

Proposal: I am considering to replace the embedded gonum.DirectedWeightedBuilder by a Graph interface that would look like:

type Graph interface {
       gonum.DirectedWeightedBuilder
       OperationCarrier
}

This would break the API which is, by now, not a problem.
What do you think?

[owulveryck]

Work in progress, see https://github.com/owulveryck/onnx-go/tree/new-interface

[owulveryck]

We should also have a look at the Operation type which is using a pointer to pb.AttributeProto; but this is declared inside an internal package...

[owulveryck]

Here is my current proposal.

I create a new interface:

// AttributesUnmarshaler is the interface implemented by types that can unmarshal  to
// themselves. AttributesUnmarshaler must copy the data if it wished to retain the data after returning.
type AttributesUnmarshaler interface {
        UnmarshalONNXAttributes(map[string]interface{}) error
}

The map[string]interface{} is a key value of the attributes; ex:

map[string]interface{}{
       "pad": []int{1,1},
      "kernel": tensor.Dense{},
}

It's simple for the type to check whether and expected value is present in the map, and the type inference shouldn't be compliated.

On top of that, I may keep this method private:

func unmarshalAttributes(attrs []*pb.AttributeProto, v interface{}) error {
        return pb.UnmarshalAttributes(attrs, v)
}

When decoding the attributes, I will first check if the Operator is fulfilling AttributesUnmarshaler, otherwise a call to unmarshalAttributes is performed. unmarshalAttributes will use the tags of the operator and this should be carefully documented.