scala.Array 如何是 Seq？
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How is scala.Array a Seq?
提问by johnmcase
I'm a strong Java developer who has very recently started trying to pick up Scala in my free time. I'm going through the Scala by ExamplePDF from scala-lang.org and am confused how the Quick Sort in the very first example works. Here is the code:
我是一名强大的 Java 开发人员，最近开始尝试在空闲时间学习 Scala。我正在浏览来自 scala-lang.org的Scala by ExamplePDF 并且对第一个示例中的快速排序是如何工作的感到困惑。这是代码：
object QuickSort extends App {
def sort(input: Array[Int]): Array[Int] = {
if(input.length <= 1) input
else
{
val pivot = input(input.length / 2)
Array.concat(
sort(input filter (pivot >)),
input filter (pivot ==),
sort(input filter (pivot <))
)
}
}
sort(Array(5, 4, 3, 2, 1)) foreach println
}
My question is not with the syntax or anything, but I am confused with where the filter function comes from. According to the PDF, it says that it comes from the Seq[T] class, and that all Arrays are instances of Seq[T]. That is all fine and dandy and while reading the PDF I was satisfied and a very happy newbie Scala developer. But then I dug a little deeper and started looking at the scaladoc for Array[T]and also the source code for Array[T] and I do not see how the Array[T] class extends or inherits the Seq[T] trait at all. What am I missing?
我的问题不在于语法或任何东西，但我对过滤器函数的来源感到困惑。根据 PDF，它说它来自 Seq[T] 类，并且所有数组都是 Seq[T] 的实例。这一切都很好，而且在阅读 PDF 时我很满意，并且是一个非常快乐的 Scala 新手开发人员。但后来我挖得更深一些，开始查看Array[T]的scaladoc 以及 Array[T]的源代码，但我没有看到 Array[T] 类如何扩展或继承 Seq[T] 特性全部。我错过了什么？
回答by Daniel C. Sobral
You are missing implicits. There's a fewquestionsabout implicitson Stack Overflow. On the PDF you are reading, see chapter 15, starting on page 113. On Scaladoc, you'll see the relevant implicits on the object scala.Predef-- just look for implicit methods which take an Arrayas input parameter and return something else.
你缺少隐式。Stack Overflow 上有一些关于隐式的问题。在您正在阅读的 PDF 上，请参阅第 15 章，从第 113 页开始。在 Scaladoc 上，您将看到对象上的相关隐式——只需查找将一个作为输入参数并返回其他内容的隐式方法。scala.PredefArray
PS: Yikes, it says Arrayis a Seq! That might have been the case before Scala 2.8, actually, but since then an Arrayis a Java Array, pure and simple.
PS：哎呀，上面写着Array是一个Seq！实际上，在 Scala 2.8 之前可能就是这种情况，但从那时起 anArray就是 Java Array，纯粹而简单。
回答by Kevin
There's an implicit conversion to WrappedArray in Predefs. See Scala Arrays vs Vectors.
在 Predefs 中有一个到 WrappedArray 的隐式转换。请参阅Scala 数组与向量。
