I tried to implement a function similar to:
def myMap[A,B](a: Seq[A], f: A => B): Seq[B] = a.map(f)
// then I want to call it like that:
myMap(List(1,13,42), _*2)
But the call to myMap doesn't compile because the compiler cannot infer the type arguments A and B. error: missing parameter type
Basically, I hoped that it would infer A (Int) given argument List(1,13,42) then infer B from given f = _*2 knowing A. But it doesn't.
What could I do to avoid writing the type arguments?
The best I found was:
def myMap[A,B](a: Seq[A], f: A => B): Seq[B] = a.map(f)
myMap(List(1,13,42), (a: Int) => a*2)
I.e. I explicitly give A in the f argument
Use multiple parameter lists.
def myMap[A,B](a: Seq[A])(f: A => B): Seq[B] = a.map(f)
// then call it like this:
myMap(List(1,13,42)) (_*2)
The collection api makes heavy use of this style for foldLeft and similar functions.
You can check the official style guide here.