Question

Forgive me if this question is a duplicate; I’m having trouble finding anything because I don’t know the right words to search. So, with implicit def, I can do things like this:

type CharsetMap = Map[Charset, Byte]

implicit def seqtup2CharsetMap(input: Seq[(String, Int)]): CharsetMap = {
  Map.empty  // placeholder
}

def somef(a: Int, b:Int, p: CharsetMap) = p
somef(1, 3, Seq(("hey", 2), ("there", 9)))

which lets me call somef with a Seq[(String, Int)] object as a parameter. The problem is that I have something like this…

def somef2(p: (CharsetMap) => Int) = p

and this does not work:

val p = (a: Seq[(String, Int)]) => 19
somef2(p)

How can I do this without doing an implicit def specifically for (Seq[(String, Int)]) => Int?

Answer 1

It looks like you want to implicitly convert some function A => B to a function that goes from C => B. You can do that with this generic implicit:

implicit def f2InputConverter[A, B, C](f: A => B)(implicit i: C => A): C => B = (c: C) => f(i(c))

Once you have that in scope, in your particular case, you’ll need an implicit function which is the inverse of the one that you’ve defined in the question:

implicit def charsetMap2Seqtup(input: CharsetMap): Seq[(String, Int)] = {
  Nil  // placeholder
}

and then you should be able to call somef2 with p