Using Tuples in map, flatmap,… partial functions

Question

If I do:

val l = Seq((\"un\", \"\"), (\"deux\", \"hehe\"), (\"trois\", \"lol\"))
l map { t => t._1 + t._2 }

It\'s ok.

If I d

Answer 1

This situation can be understand with the types of inner function.

First, the type syntax of parameter function for the map function is as follows.

Tuple2[Int,Int] => B //Function1[Tuple2[Int, Int], B]

The first parameter function is expand to this.

(t:(Int,Int)) => t._1 + t._2 // type : Tuple2[Int,Int] => Int

This is ok. Then the second function.

(t:(Int, Int)) => t match {
  case (a:Int, b:Int) => a + b
}

This is also ok. In the failure scenario,

(a:Int, b:Int) => a + b 

Lets check the types of the function

(Int, Int) => Int // Function2[Int, Int, Int]

So the parameter function type is wrong.

As a solution, you can convert multiple arity functions to tuple mode and backward with the helper functions in Function object. You can do following.

val l = Seq(("un", ""), ("deux", "hehe"), ("trois", "lol"))
l map(Function.tupled((b, n) => b + n ))

Please refer Function API for further information.