Is it possible to express kotlin 'with' method equivalent in Scala?

Question

Kotlin Standard lib contains the 'with' method that receives an object and a method of that object defined as:

public inline fun <T, R> with(receiver: T, block: T.() -> R): R = receiver.block()

And can be used as:

val str = "string"
with(str) {
  println(size)) // will print 6; equals to "string".size
  println(substring(3)) // will print (ing); equals to "string".substring(3)
}

How to define similar method in Scala?

Answer 1

There is no way to define such a method in Scala, because the concept of function literals with receiver does not exist in Scala.

However, Scala's import is general enough that you can use it instead of with. Your example would write as:

val str = "string"
import str._
println(length)
println(substring(3))

Note that size specifically does not work with this scheme because it happens to be implicitly pimped on String, so I had to use length instead. However, in general, this is the pattern we use.

Edit after comment: if you want to explicitly scope the import to a portion of your code, you can do so with braces, which are always allowed to scope things:

val str = "string"

{
  import str._
  println(length)
  println(substring(3))
}
println(length) // does not compile

Note that the blank line is necessary, otherwise it will be parsed as trying to call the apply method on "string" with the {...} as argument. To avoid this problem, you can use the locally method:

val str = "string"
locally {
  import str._
  println(length)
  println(substring(3))
}
println(length) // does not compile

locally per se doesn't do anything; it is only used to visually highlight that the braces are there only for scoping reasons, and by extension to help parsing do the right thing.