"使用"语句相当于Scala？

Question

也许是从Scala学习者那里闲聊,但是...在我的修补中我写了以下内容:

( n.child.size > 0 ) && ( n.child.filter( ! _.isInstanceOf[Text] ).size == 0 )

('n'是一个scala.xml.Node,但这并不重要.也不是特定的逻辑.)

两次打电话给孩子()并不是那么好,所以我打算改变它:

val list = n.child
( list.size > 0 ) && ( list.filter( ! _.isInstanceOf[Text] ).size == 0 )

但考虑到我已经非常欣赏能够过滤()和map()等而不需要声明中间变量,我立即发现这很臭.它就是......所以......所以Java-ish!:p

唉,通过搜索SO和谷歌以及ScalaDocs(特别是Any和AnyRef)和The Book已经找不到合适的东西.我希望也许是这样的:

n.child{ list => ( list.size > 0 ) && ( list.filter( ! _.isInstanceOf[Text] ).size == 0 ) }

甚至

n.child.with{ list => ... }

这样的事情存在吗？或者我只是陷入了一种不变的热情？

Answer 1

{
    import n.child._
    ( size > 0 ) && ( filter( ! _.isInstanceOf[Text] ).size == 0 )
}

Answer 2

"with" is, of course, a reserved word in Scala, so let's call it "let", from the similar binding form in Lisp and Haskell. Turns out "let" is just a backwards way of writing function application.

def let[A,B](param:A)(body: A=>B):B = body(param)

let(n.child){list=> ...}

If the bound variable is used only once, you could of course use the anonymous function form, but that defeats the purpose.

Answer 3

class Tap[A](underlying:A){
   def tap[B](func: A=>B) = func(underlying)
}

implicit def anyToTap[A](underlying:A)=new Tap(underlying)

n.child.tap{x =>
   ( x.size > 0 ) &&
   ( x.filter( ! _.isInstanceOf[Text] ).size == 0 )
}