Extension methods for current scope

[scf37]

Motivation

I want to have concise collection builders like:

import stuff.buildList
// import stuff.add    <-- avoid importing DSL impementation
val l: List[String] = buildList {
  add("a")
  add("b")
}

Solution

Extension methods for current scope in the form b instead of a.b - they can be made available in specific scopes via givens therefore avoiding magic imports.

extension() {
  def hello() = println("hello")
}

hello()

Implementation

// implementation
import scala.collection.mutable

class BuilderContext[A](val b: mutable.Buffer[A] = mutable.Buffer.empty[A]):
  // empty argument list - extension for current scope available while implicit BuilderContext is in scope
  extension[A]() { 
    def add(v: A): Unit = b.b += v
  }

inline def buildList[A](inline f: BuilderContext[A] ?=> Unit): List[A] = {
  given b: BuilderContext[A] = BuilderContext[A]()
  f
  b.b.toList
}