How to make two function parameters as implicit

Question

Assume we have Object that takes function as parameter of apply method:

object Wrapper {
  def apply(block: TypeA => String) = {
    TypeA a = ...
    block(a)
  }
}

TypeA is domain type of application.

Now when I define inline block I can define TypeA parameter as implicit:

Wrapper { implicit a => functionThatUseImplicitA() }

But what if block parameter is not Function1, but Function2? How can I define both parameters as implicit?

object Wrapper2 {
  def apply(block: (TypeA, TypeB) => String) = {
    TypeA a = ...
    TypeB b = ...
    block(a, b)
  }
}

This one does not work:

Wrapper { implicit (a, b) => functionThatUseImplicitAB() }

The only workaround is define them as vals:

Wrapper { (a, b) => 
  implicit val ia = a
  implicit val ib = b
  functionThatUseImplicitAB()
}

Thanks!

senia · Accepted Answer · 2013-06-25T12:01:55.607

8

According to the SLS 6.23 Anonymous Functions implicit keyword is allowed only for single argument functions:

Expr ::= (Bindings | [‘ implicit ’] id | ‘_’) ‘=>’ Expr
ResultExpr ::= (Bindings | ([‘ implicit ’] id | ‘_’) ‘:’ CompoundType) ‘=>’ Block

So you can't make two function parameters as implicit.

This is the one of reasons to use curried functions:

object Wrapper {
  def apply(block: TypeA => TypeB => String) = ???
}

Wrapper { implicit a => implicit b =>
  functionThatUseImplicitAB()
}

edited Jun 25 '13 at 12:01

answered Jun 25 '13 at 11:56

senia

Could you please tell me how to solve this issue with curried functions? functionThatUseImplicit* are from external API – 1esha Jun 25 '13 at 11:57
@AlexeyRomantchouk: I've updated my answer. It solves your problem when you can change definition of `Wrapper`. – senia Jun 25 '13 at 12:00

1 Answers1