make SummingCache a trait and provide multiple implementations that can be picked based on the monoid implementation

[julienledem]

In particular whether plus or sumOption is more efficient.

[jcoveney]

this is equivalent to .reduce(_ && _)

[jcoveney]

I do not love this approach. I don't like the idea that all monoids have to now tag themselves with anything that might be useful to caching...I would vastly prefer for these two to be decoupled. It IS possible to do this with typeclass, but the syntax gets pretty nasty when you want to do it on Semigroup[T].

[julienledem]

The main idea is that depending on the Monoid implementation either calling plus or sumOption will be more efficient and that's a characteristic of the Monoid.
I'm trying to find a good way for the Monoid to advertise this property. Suggestions welcome.

Another simpler option is to add a method in Semigroup which will return plus as the preferred summing mechanism. Monoids implementing sumOption or sum could override it and indicate sumOption is prefered instead.

[jcoveney]

Is there a compelling example right now where not having this makes something else particularly bad or ugly?

[ianoc]

Sorry my bad, git foo on cmd line broke stuff and closed all of these

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