class Foo {
  implicit def pair2fun2[A, B, C](f: (A, B) => C) = 
     {p: (A, B) => f(p._1, p._2) }

  def foo(f: ((Int, Int)) => Int) = f
  def bar(x: Int, y: Int) = x + y 

  foo({ (x: Int, y: Int) => x + y }) // works
  foo(pair2fun2(bar)) // works
  foo(bar _) // error
  foo(bar)   // same error
}

/home/iuliandragos/sandbox/views.scala:10: error: missing arguments for method bar in class Foo;
follow this method with `_' if you want to treat it as a partially applied function
  foo(bar _) // error
      ^
/home/iuliandragos/sandbox/views.scala:11: error: missing arguments for method bar in class Foo;
follow this method with `_' if you want to treat it as a partially applied function
  foo(bar)   // same error
      ^
two errors found