定义Scala匿名函数时可以使用块吗？

Question

I have this method:

def myMethod(value:File,x: (a:File) => Unit) = {
   // Some processing here
   // More processing
   x(value)
}

I know I can call this as:

myMethod(new File("c:/"),(x:File) => println(x))

Is there a way I could call it using braces? Something like:

myMethod(new File("c:/"),{ (x:File) =>
     if(x.toString.endsWith(".txt")) {
         println x
     }
})

Or do I have to write that in another method and pass that to myMethod ?

Answer 1

The body part of the function can be a block enclosed in braces:

myMethod(new File("c:/"), x => { 
  if (x.toString.endsWith(".txt")) {
    println(x) 
  }
})

An alternative is way to define myMethod as a curried function:

def myMethod(value: File)(x: File => Unit) = x(value)

Now you can write code like the following:

myMethod(new File("c:/")) { x => 
  if (x.toString.endsWith(".txt")) {
    println(x) 
  }
}

Answer 2

The example you gave actually works, if you correct the lack of parenthesis around x in println x . Just put the parenthesis, and your code will work.

So, now, you might be wondering about when you need parenthesis, and when you don't. Fortunately for you, someone else has asked that very question .