WeightedEdge abstraction

[trs123]

Java seems not to have an abstraction of numbers or arithmetic values.

I first thought that the class Numbers would fill this role and designed a WeightedEdge<V, W extends Number> like this

public interface WeightedEdge<V, W extends Number> {
    W weight();
}

but this does not allow to formulate calculations with the weights, i.e. something like

public interface WeightedPath<V, E extends WeightedEdge<V, W>, W extends Number> 
    extends Path<V, E> {

    default W distance() {
        // Problem: Number.plus() does not exist
        return edges().reduce((sum, edge) -> sum.plus(edge.weight())); 
    }
}

So do we have to declare WeightedEdge to always use double for weights??

[monora]

(In reply to comment #0)

So do we have to declare WeightedEdge to always use double for weights??

That is how JGraphT does it (see DefaultWeightedEdge). I think this ok, since every metric on a graph is a mapping V x V -> real numbers.

[trs123]

Double is not really satisfying, as I can easily imagine integers, magnitudes with units or even more abstract magnitudes as weights. Of course you can say this can be mapped to real numbers, unfortunately doubles are not real numbers: just think of the problems with precision that doubles have.
Furthermore you just lose type information when doing this mapping.

So I'm not pleased with limiting weights to doubles at all :-(