How to apply a function to a tuple?

Question

This should be an easy one. How do I apply a function to a tuple in Scala? Viz:

scala> def f (i : Int, j : Int) = i + j
f: (Int,Int)Int

scala> val p = (3,4)
p:          


        

Answer 1

In Scala 2.8 and newer:

scala> def f (i : Int, j : Int) = i + j
f: (i: Int,j: Int)Int

// Note the underscore after the f
scala> val ff = f _
ff: (Int, Int) => Int = <function2>

scala> val fft = ff.tupled
fft: ((Int, Int)) => Int = <function1>

In Scala 2.7:

scala> def f (i : Int, j : Int) = i + j
f: (Int,Int)Int

// Note the underscore after the f
scala> val ff = f _
ff: (Int, Int) => Int = <function>

scala> val fft = Function.tupled(ff)
fft: ((Int, Int)) => Int = <function>

Answer 2

In Scala 3, you can use TupledFunction:

For a single use, you can do

summon[TupledFunction[(Int, Int) => Int, ((Int, Int)) => Int]].tupled(f)((2, 3))

To make it easier to use, you can use an extension (copied from Dotty's own documentation)

extension [F, T <: Tuple, R](f: F)(using tf: TupledFunction[F, T => R])
  def tupled(t: T): R = tf.tupled(f)(t)

And then you can do f.tupled((2, 3)) to get 5.

Answer 3

Scala 2.13

def f (i : Int, j : Int) = i + j

import scala.util.chaining._
(3,4).pipe((f _).tupled)   //res0: Int = 7

Answer 4

Following up on the other answer, one could write (tested with 2.11.4):

scala> def f (i: Int, j: Int) = i + j
f: (i: Int, j: Int)Int

scala> val ff = f _
ff: (Int, Int) => Int = <function2>

scala> val p = (3,4)
p: (Int, Int) = (3,4)

scala> ff.tupled(p)
res0: Int = 7

See def tupled: ((T1, T2)) ⇒ R:

Creates a tupled version of this function: instead of 2 arguments, it accepts a single scala.Tuple2 argument.

Answer 5

scala> def f (i: Int, j: Int) = i + j
f: (i: Int, j: Int)Int
scala> val p = (3,4)
p: (Int, Int) = (3,4)
scala> val ft = (f _).tupled
ft: ((Int, Int)) => Int = <function1>
scala> ft apply(p)
res0: Int = 7