Partial Functions as an input parameter in scala - scala

Question

I am trying to pass the partial function as input to square function.
What is worng with the following code?
package PartialFunction
object PartialFunctionSum {
val yourConstant = 10
val pf: PartialFunction[(Int, Int), Int] = {
case (x, y) => x + y + yourConstant
}
def square(cb:(Int, Int) => Int): Unit = {
println(cb(5,10))
}
def main(args: Array[String]): Unit= {
square(pf)
}
}

Answer 1

A PartialFunction is a Function1 (a => b) and square needs a Function2 ((a,b) => c)
One way to accomplish what you want to do is changing cb type to Function1.
object PartialFunctionSum extends App {
val yourConstant = 10
val pf: PartialFunction[(Int, Int), Int] = {
case (x, y) => x + y + yourConstant
}
def square(cb:((Int, Int)) => Int): Unit = {
println(cb(5,10))
}
square(pf)
}
Also, anywhere where you need a FunctionX, you can define a PartialFunction, so
square {
case (x, y) => x + y + yourConstant
}
Or transform your PartialFunction in a Function2 with a lambda
square( pf.apply(_, _) )

Answer 2

Anywhere you need a function you can a pass a PartialFunction,
Your problem is with square definition:
def square(cb:(Int, Int) => Int): Unit = {
println(cb(5,10))
}
That means that cb is a function that receives two Ints and returns another Int.
Just change square signature as follows:
def square(cb: ((Int, Int)) => Int): Unit = {
println(cb(5 -> 10))
}
And now your types are compatible and the rest of your code works as you expected.

Answer 3

(Int, Int) => Int is an instance of Function2[Int, Int, Int](a Function that takes 2 Int parameters and returns an Int), not PartialFunction[(Int, Int), Int] (a partial function that takes an input of type (Int, Int) and returns an Int)
If you want to pass your parameters as a Tuple then:
def square(cb:PartialFunction[(Int, Int),Int]): Unit = {
println(cb((5,10)))
}
Example:
def square(cb:PartialFunction[(Int, Int),Int]): Unit = {
println(cb((5,10)))
}
square: (cb: PartialFunction[(Int, Int),Int])Unit
scala> square{case (i, j) => i * j}
50