Scala中的隐式函数类型

Question

Recently, I have become interested in implicit functions. In the documentation , we can see several examples of using this property, but I think I do not quite understand how it works.

For example, we can read that implicit T0 => R is actually

trait ImplicitFunction1[-T0, R] extends Function1[T0, R] {
  override def apply(implicit x: T0): R
}

After writing the function below

val func = {implicit x: Int => 2*x}

I tried to use it in this way

implicit val x: Int = 3
println(func)

But it doesn't seem to work (only the <function1> type is returned, it looks like apply hasn't been used at all). If I had a method for it, it would work fine

def func(implicit x: Int) = 2*x

I'm not sure what I'm missing here.

Answer 1

Implicit function types work in Dotty

https://dotty.epfl.ch/docs/reference/contextual/implicit-function-types.html

https://dotty.epfl.ch/blog/2016/12/05/implicit-function-types.html

In Scala 2 func has type Int => Int instead of absent implicit Int => Int (aka given Int => Int ).

implicit x: Int => ??? is just a shorthand for x: Int => { implicit val _x: Int = x; ???} x: Int => { implicit val _x: Int = x; ???} .

Out of all new implicit (aka given ) features in Dotty only by-name implicits were backported to Scala 2.13.0.