Add Pair-based edges initializer to Graph types

[bwetherfield]

Like so, so that the edge type is constructed internally...

WeightedGraph<Tendency,Int>(
        [
            .up,
            .down
        ],
        [
           (.up,.up): 1,
           (.down,.down): 1
        ]
    )

at the moment we have to do:

WeightedGraph<Tendency,Int>(
        [
            .up,
            .down
        ],
        [
            UnorderedPair(.up,.up): 1,
            UnorderedPair(.down, .down): 1
        ]
    )

[jsbean]

I think this would require an initializer like so:

extension WeightedGraph where Node == Tendency, Weight == Int {
    init <D> (_ nodes: Set<Tendency>, _ dictionaryLiteral: D) where D: DictionaryLiteral, where D.Element == (Tendency,Int) 
    {
        ...
    }
}

[jsbean]

See DictionaryLiteral and KeyValuePairs.

You can't actually pass a real dictionary in, because tuples are not Hashable 🤦‍♂️ .

[jsbean]

But if this is for syntax sugar, then you can use the DictionaryLiteral syntax.

Give it a try. No guarantees here.

[bwetherfield]

Oh! Totally forgot about Hashability!

[jsbean]

But KeyValuePairs doesn't actually require Hashable conformance :o, I am pretty sure.

[jsbean]

You would need to do something like:

extension WeightedGraph {
    init (_ nodes: Set<Tendency>, _ keyValuesPairs: KeyValuePairs<Node,Weight>) {
        self.init(nodes, Dictionary(keyValuePairs.lazy.map { k,v in (UnorderedPair(k.0, k.1), v) })
    }
}