Scala: Is it a closure?

Question

I want to know does my code represent a closure concept ?

object Closure {
  val fun = (x: Int) => x + 1
  def clj = (y: Int) => y * fun(y)
}

Here is my runner code.

object App {
  def main(args: Array[String]) {
    val c = Closure
    val result = c.clj(10)
    println(result)
  }
}

Suppose, the closure code is

def clj = (y: Int) => y * fun(y)

Or maybe I'm wrong?

Answer 1

It isn't, because it doesn't close over anything.

This would be a closure:

object Foo {
  def clj(a: Int) = { (b: Int) => a + b }
}

This is:

• An object called Foo ...
• that contains a function clj() ...
• that returns another function.

The returned inner function captures (or closes over ) the value of a at the time clj() is called, conceptually keeping it alive.

Thus:

val f1 = Foo.clj(10) // returns a function that adds 10 to whatever is passed
f1(100)              // => 110

The Wikipedia entry on closures actually contains a decent description of the concept.

https://en.wikipedia.org/wiki/Closure_(computer_programming)

Answer 2

在我看到闭包概念时，是的，您在clj的代码表示闭包，因为它引用了外部函数fun ，即闭包术语中的所谓“环境”。