spiffman spiffman - 1 year ago 99
Scala Question

Keeping named and default parameters when assigning a function

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.


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 Source

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") = 

You can avoid duplication using

object imports {
  val x = myproject.somepackage

// elsewhere
import myproject.imports._


// or
import myproject.imports.x._


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

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