Rewrite SAM

[gabro]

Not sure this can be fully automated, but since Scala 2.12 has support for SAM some rewrite like this should be possible:

Given

trait SomeSAM {
  def foo(x: Int)
}

Then this

val aSam = new SomeSAM {
  def foo(x: Int) = x
}

can become (in Scala 2.12)

val aSam: SomeSAM = (x: Int) => x

[olafurpg]

This is a cool idea! I think we will need Type.members to implement this rewrite because iiuc then the SAM type must have only one method?

val aSam = (x: Int) => x

Should that be val aSam: SomeSAM = (x: Int) => x?

[gabro]

Correct, SAMs must have only one method (SAM stands for Single Abstract Method), and yes, I think the type annotation is required.

[gabro]

So a plan for this could be:

• look for instantiations of traits new SomeTrait { ... }
• check in the semanticdb that SomeTrait defines a single abstract method (not sure how doable this is in case of trait inheritance)
• replace the trait with a function (this is easy)

I'm not sure how many edge cases we're going to cover, but it should be ok, since we would probably not generating false positives. Simply, some patterns would go unrecognized and lead to empty patches. I think this is worth a shot.

[MasseGuillaume]

I'm starting to work on this. #552

The spec for the SAM conversion is defined here: http://www.scala-lang.org/files/archive/spec/2.12/06-expressions.html#sam-conversion

[olafurpg]

This is a good idea. After the PR #827, we are moving most built-in rules outside of the scalacenter/scalafix repository so that they can evolve at a different pace than Scalafix APIs. As long as a custom rule meets a certain level of quality, it can still

• be automatically be included by sbt-scalafix
• have tab completion in the sbt shell like built-in rules
• be documented on the main Scalafix website

Ping us on Gitter if you believe your rule is good enough for inclusion. Don't hesitate to ask for help around code review or general guidance on writing/sharing custom rules.

[joroKr21]

Does this rule exist somewhere now?

[bjaglin]

Does this rule exist somewhere now?

Unfortunately not, to my knowledge.

[joroKr21]

Unfortunately not, to my knowledge.

Thanks, I would like to have it so if I come up with something useful I will post back here 👍