@Override
    public PrimitiveTensorFunction<NAMETYPE> toPrimitive() { return this; }
Creates a value function

@param argument the tensor to return a cell value from
@param subspaceAddress a description of the address of the cell to return the value of. This is not a TensorAddress
                       because those require a type, but a type is not resolved until this is evaluated
vespajlib/src/main/java/com/yahoo/tensor/functions/Slice.java