PRE SIP: ThisFunction | scope injection (similar to kotlin receiver function)

Language Design
73

Perhaps I’ve written it somewhere else, but IMO scope injection would make tests much better.

Consider this code:

package scope

import java.io.Closeable
import java.nio.file.{Files, Path}

import org.scalatest.{FlatSpec, MustMatchers}

class FixturesDemoSpec extends FlatSpec with MustMatchers {
  behavior of "something"

  it must "do thing 1" in test(1, "a") { fixture =>
    import fixture._
  // test body
  }

  it must "do thing 2" in test(2, "b") { fixture =>
    import fixture._
  // test body
  }

  it must "do thing 3" in test(3, "c") { fixture =>
    import fixture._
  // test body
  }

  class Fixture(val resource: Any, val service: Any, val tempDir: Any)

  def test(arg1: Int, arg2: String)(body: Fixture => Unit): Unit = {
    val resource: Closeable = ???
    val service: Closeable  = ???
    val tempDir: Path       = ???
    try {
      body(new Fixture(resource, service, tempDir))
    } finally {
      resource.close()
      service.close()
      Files.delete(tempDir)
    }
  }
}

Assuming average test body is just a few lines then additional import fixture._ makes code a bit clumsy.

Replacing this:

  it must "do thing 1" in test(1, "a") { fixture =>
    import fixture._
  // test body
  }

with:

  it must "do thing 1" in test(1, "a") { this =>
  // test body
  }

would make tests much more elegant (no repetition) and somewhat more readable.

I don’t see how implicit functions, implicit conversions, etc would replace scope injection without adding a lot of bloat (effectively making that pointless).