CODEWITHSUNDEEP
scala
fe2s
fe2s

Reputation: 435

converting method to function?

1) How is this construction called? Cannot google it.

2) Why it doesn't work? I expect message be printed. 

class A {
  def m() {
    println("m()")
  }
}

object Main {

  def main(args: Array[String]) {
    val fun = (_: A).m _
    fun(new A())
  }

}

Upvotes: 1

Views: 194

Answers (1)

Randall Schulz
Randall Schulz

Reputation: 26486

As om-nom-nom says, the conversion of methods to functions is called "partial application." It can be expressed explicitly by using underscore(s) as "arguments" to a method or automatically by the compiler when the available type information is sufficient for it to infer that a method name used in a place where a function is required can be partially applied to produce the required function.

Now, for your code. As written, the result of the call fun(new A()) is a Function1[Unit, Unit]. You'd have to apply that function to get the println invoked

// Exiting paste mode, now interpreting.

defined class A
defined module Main

scala> Main.main(Array())

scala> def doIt { val fun = (_: A).m _; fun(new A())() }
doIt: Unit

scala> doIt
m()

Upvotes: 1

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