API change suggestions about elastic4s

[guersam]

If you agree I'll open a draft PR.

[sksamuel]

Shall we do these in separate PRs ?

What's the advantage of bringing the inner classes to top level?

[guersam]

1. At first, I'd like to point out inner classes become different concrete ones according to the class hierarchy, for example:

   trait A { case class Inner(v: Int) }
   object B extends A
   object C extends A
   
   B.Inner(1) == B.Inner(1) // true
   B.Inner(1) == C.Inner(1) // false

   It's because B.A and C.A have different FQCNs. Single FQCN has following benefits other than equality checking:

2. Implicit resolution without import tax

   class RichInt(a: Int) {
     def plus(b: Int) = a + b
   }
   
   object RichInt {
     implicit def apply(a: Int): RichInt = new RichInt(a)
   }
   
   def plus1(a: RichInt) = a.plus(b)
   
   plus1(23) == 24 // true 

   We still need import RichInt._ to directly use 1.plus(3), so we need to exposure some implicit conversions for the entry points at least. But after that we can provide well-organized implicit conversions as well as type safety.

   I used this technique for Redisreact to provide typesafe, out-of-box serialization not relying on (_: Any).toString. I'd like to bring it to Elasitc4s as well in near future.

3. Avoid boxing/unboxing overhead using Value classes

   By extending AnyVal we can avoid runtime overhead caused by creating tons of intermediate wrapper instances. However, it's not supported for inner classes:

   scala> class A
   // defined class A
   
   scala> class B(val a: A) extends AnyVal
   // defined class B
   
   scala> class Outer { class C(val a: A) extends AnyVal }
   //<console>:8: error: value class may not be a member of another class
   //       class Outer { class C(val a: A) extends AnyVal }
   //                           ^

[guersam]

Actually it's not necessary to make it top-level, the point is to give it single FQCN. So it's ok in the previous example:

object Outer { class C(val a: A) extends AnyVal }
// it works because there's only one FQCN for `Outer.C`

[sksamuel]

Ok I see. What classes are you wanting to be top level? Happy for you to do a PR.

[guersam]

Couldn't check all of them yet, but basically want to avoid any unnecessary path-dependent class.

I'll do a draft in one or a few weeks, so let's discuss more on that PR.

[sksamuel]

Ok lets do that. 0.90.4 is out this week or next so will be doing the next release for that.