Monoid for case class?

[Ian Hummel]

Hey guys,

Is there a way to get a monoids "automatically" for a case class, assuming each component of the case class has a monoid?

For example,

case class Impressions(load: Long, uniques: HLL)

There are monoids for both Long and HyperLogLog... so can I get a Monoid[Impressions] somehow (without the boilerplate of implementing it myself)?  I think this is what the ProductXMonoids do, but wasn't clear exactly how to wrangle the right implicit into scope.

Cheers!

[Oscar Boykin]

Yes, this is what the product implicits are for, and yes it is still a pain. When we switch to 2.10 only, this can be done with a macro, and we will add that.

you should do:

scala> import com.twitter.algebird.Semigroup

import com.twitter.algebird.Semigroup

scala> case class Test(x: Int, y: String)

defined class Test

scala> Semigroup.apply(Test.apply _, Test.unapply _)

res1: com.twitter.algebird.Semigroup[Test] = com.twitter.algebird.Product2Semigroup@730476e8

scala> res1.plus(Test(1, "hello"), Test(2, "world"))

res2: Test = Test(3,helloworld)

The apply, unapply line is unfortunate, but oh well.

What I want is a default implicit macro that can build these for any case class. Pull req?

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Oscar Boykin :: @posco :: http://twitter.com/posco