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Scala implicit parameter and Japanese emoticon 'foldLeft'

I am currently learning Scala, but there are still so many things I just don't understand ...

So, I was accidentally looking for a stack overflow when the wild answer popped up : https://stackoverflow.com/a/446873/stackoverflow

This answer uses an implicit parameter and a foldLeft function with a - yes it looks like one - a Japanese smiley face. source code of question:

class Account(implicit transactionLog: TransactionLog) {
  def balance = transactionLog.foldLeft(_ + _)
}

class TransactionSlip(from: Account, to: Account, amount: BigDecimal)

What exactly does the implicit keyword mean in this case? What does an emoticon do? I just don't get it from the fragments floating around ...

Thanks in Advance.

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1 answer


Two answers:



  • _ + _

    is a placeholder for a function that takes two arguments and adds them . The underscore is here to mark the position of the argument in such syntax. You can read this for all kinds of underscore uses in Scala.

  • the keyword implicit

    denotes an implicit argument . This means that in the places where you need Account

    , you can provide a constructor without explicitly specifying the corresponding one transactionLog

    , which will be grabbed from the context.

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