带有关键字使用的 Scala
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Scala with keyword usage
提问by den bardadym
I found simple example:
我找到了一个简单的例子：
class Post extends LongKeyedMapper[Post] with IdPK {
def getSingleton = Post
object title extends MappedText(this)
object text extends MappedText(this)
object date extends MappedDate(this)
}
object Post extends Post with LongKeyedMetaMapper[Post] {
def getPosts(startAt: Int, count: Int) = {
Post.findAll(OrderBy(Post.date, Descending), StartAt(startAt), MaxRows(count))
}
def getPostsCount = Post.count
}
What does it mean with IdPK?
这是什么意思with IdPK？
Thanks.
谢谢。
回答by Jonas
withmeans that the class is using a Trait via mixin.
with意味着该类正在通过mixin使用 Trait 。
Posthas the Trait IdPK(similar to a Java class can implementsan Interface).
Post具有 Trait IdPK（类似于 Java 类可以implements是接口）。
回答by Colin Woodbury
While this isn't a direct answer to the original question, it may be useful for future readers. From Wikipedia:
虽然这不是对原始问题的直接回答，但它可能对未来的读者有用。来自维基百科：
Scala allows to mix in a trait (creating an anonymous type) when creating a new instance of a class.
Scala 允许在创建类的新实例时混合使用特征（创建匿名类型）。
This means that withis usable outside of the top line of a class definition. Example:
这意味着它with可以在类定义的顶行之外使用。例子：
trait Swim {
def swim = println("Swimming!")
}
class Person
val p1 = new Person // A Person who can't swim
val p2 = new Person with Swim // A Person who can swim
p2here has the method swimavailable to it, while p1does not. The realtype of p2is an "anonymous" one, namely Person with Swim. In fact, withsyntax can be used in any type signature:
p2这里有swim可用的方法，而p1没有。的真实类型p2是“匿名”类型，即Person with Swim. 事实上，with语法可用于任何类型签名：
def swimThemAll(ps: Seq[Person with Swim]): Unit = {
ps.foreach(_.swim)
}
EDIT (2016 Oct 12):We've discovered a quirk. The following won't compile:
编辑（2016 年 10 月 12 日）：我们发现了一个怪癖。以下不会编译：
// each `x` has no swim method
def swim(xs: Seq[_ >: Person with Swim]): Unit = {
xs.foreach(_.swim)
}
Meaning that in terms of lexical precedence, withbinds eagerly. It's _ >: (Person with Swim), not (_ >: Person) with Swim.
这意味着就词汇优先级而言，with热切地绑定。是_ >: (Person with Swim)，不是(_ >: Person) with Swim。
