CODEWITHSUNDEEP
scalaenrich-my-library
Rafael de F. Ferreira
Rafael de F. Ferreira

Reputation: 488

How to implicitly extend a Function without losing type inference

For a DSL I need to implicitly extend function values. For instance:

trait PimpedFunction[-A, +B] extends Function1[A, B] {
  def foo = 42
}

object PimpedFunction {
  implicit def pimp[A, B](f: Function1[A, B]): PimpedFunction[A, B] = 
    new PimpedFunction[A, B] {
      def apply(a: A) = f(a)
    }
}

A function that uses PimpedFunction could be defined as something like:

def takes(f: PimpedFunction[String, Int]) = f.foo

The problem is on the code that calls takes. The following works as expected:

takes((_: String).size)

But if I elide the parameter type the compile fails to infer it:

takes(_.size)

Can I change anything in order to help scalac's inference?

OBS: The real use case is related to this: https://gist.github.com/xeno-by/4542402

Upvotes: 0

Views: 85

Answers (1)

Rex Kerr
Rex Kerr

Reputation: 167891

If you can allow your takes function to do the conversion itself, it'll work:

def takes(f: Function1[String, Int])(
  implicit f2pf: Function1[String,Int] => PimpedFunction[String,Int]
) = f2pf(f).foo

(you can overload takes to take either a PF or a regular function).

Upvotes: 3

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