ShowOrToString

If you are using the Cats library, you can define a Show type class for any data type.

Scala 3

// Simplified definition.
// See https://typelevel.org/cats/typeclasses/show.html for further details
trait Show[T]:
  def show(t: T): String

Scala 2.13

// Simplified definition.
// See https://typelevel.org/cats/typeclasses/show.html for further details
trait Show[T] {
  def show(t: T): String
}

The Show type provides a String representation of an object, guaranteed to be a deliberate choice instead of the default toString() defined on every JVM object.

Sounds great! We should use it... if it is defined.

But maybe this is not critical to our logic. Maybe we are logging, within a greater algortithm, and which to use the Show representation when it is defined. But if it isn't, we can accept falling back to the default toString() method.

Scala 3

// With Show
log.info("We diddled the doodle using " + Show.show(someObject))

// Without Show
log.info("We diddled the doodle using " + someObject.toString)

Scala 2.13

// With Show
log.info("We diddled the doodle using " + Show.show(someObject))

// Without Show
log.info("We diddled the doodle using " + someObject.toString)

This sounds like an optional given!

Scala 3

if (CouldBeGiven[Show[SomeObject]].isGiven) {
  // use Show
} else {
  // use toString
}

Scala 2.13

if (CouldBeGiven[Show[SomeObject]].isGiven) {
  // use Show
} else {
  // use toString
}

In fact, the couldbe-cats package provides a ready implementation of ShowOrToString:

Scala 3

trait ShowOrToString[-A: CouldHave[Show]]:
  def s(a: A): String = CouldHave[Show, A].act(_.show(a))(a.toString)

Scala 2.13

trait ShowOrToString[-A](implicit A: CouldHave[Show, A]) {
  def s(a: A): String = CouldHave[Show, A].act(_.show(a))(a.toString)
}

which allows you to simplify the logic to:

Scala 3

def yourFunction[A: ShowOrToString](a: A):
  // ...
  log.info("We diddled the doodle using " + ShowOrToString.s(someObject))
  // ...

Scala 2.13

def yourFunction[A: ShowOrToString](a: A) {
  // ...
  log.info("We diddled the doodle using " + ShowOrToString.s(someObject))
  // ...
}