Keeping named and default parameters when assigning a function

Question

When assigning a function using an unapplied method, it appears that named and default parameters are lost. Is there any way to avoid this?

def foo(namedParam: String = "defaultValue") = namedParam*2
// scala> foo()
// res8: String = defaultValuedefaultValue

def bar = foo _
// scala> bar()
// <console>:28: error: not enough arguments for method 
//               apply: (v1: String)String in trait Function1. 
//               Unspecified value parameter v1.

The reason I want to do this is to bundle my imports in a single file, i.e.

myproject/imports.scala

object imports {
  def externalAPIFunction = myproject.somepackage.internalFunction _
}

scala shell

import myproject.imports._

externalAPIFunction() // no named or default arguments :(

Any way to do this or do I have to put my default arguments in the external function definition?

Answer 1

Functions (i.e. values of type Function<N>[...]) simply can't have default or implicit parameters in Scala, only methods can. And method _ returns a function: that's what it's for. So yes, to achieve your purpose you'd need to write

object imports {
  def externalAPIFunction(namedParam: String = "defaultValue") = 
    myproject.somepackage.internalFunction(namedParam)
}

You can avoid duplication using

object imports {
  val x = myproject.somepackage
}

// elsewhere
import myproject.imports._

x.internalAPIFunction()

// or
import myproject.imports.x._

internalAPIFunction()

which may or may not be good enough for your purposes.