问题描述
我被这前pression猝不及防：
I was caught off guard by this expression:
val words = strings.map(s => s.split(",")) // split CSV data
val nonHashWords = words.filter(word => word.startsWith("#"))
这建筑是错误的，因为字是顺序[数组[字符串]] 而不是intented 序列[字符串] 。
我没想到的是阵列将有一个 startsWith 的方法，所以我打了一下它，了解它的语义。我自然希望这是真的：阵列（你好，世界）startsWith（你好）
This construction is faulty, as words is a Seq[Array[String]] instead of the intented Seq[String].I didn’t expect that Array would have a startsWith method, so I played a bit with it to understand its semantics. I naturally expected this to be true: Array("hello", "world").startsWith("hello")
下面是我探索会话的其余部分：
Here’s the rest of my exploration session:
scala> val s = Array("hello","world")
s: Array[String] = Array(hello, world)
scala> s.startsWith("hello")
res0: Boolean = false
scala> s.startsWith("h")
res1: Boolean = false
scala> val s = Array("hello","hworld")
s: Array[String] = Array(hello, hworld)
scala> s.startsWith("h")
res3: Boolean = false
scala> s.startsWith("hworld")
res4: Boolean = false
scala> s.toString
res5: String = [Ljava.lang.String;@11ed068
scala> s.startsWith("[L")
res6: Boolean = false
scala> s.startsWith("[")
res7: Boolean = false
什么是array.startsWith预期的行为？
What is the expected behavior of ‘array.startsWith’ ?
推荐答案
以下文档：
DEF startsWith [B]（即：GenSeq [B]）：Boolean测试这是否可变
索引序列开始与给定的序列
所以 array.startsWith（X）期望 X 是一个序列。
So array.startsWith(x) expects x to be a sequence.
scala> val s = Array("hello","world")
scala> s.startsWith(Seq("hello"))
res8: Boolean = true
会发生什么事在上面的问题是，作为参数传递的字符串作为字符序列进行评估。这导致编译器错误虽然在特定情况下，它不会产生预期的结果。
What happens in the question above is that the string passed as parameter is evaluated as a sequence of characters. That leads to no compiler error although in that specific case it will not yield the expected result.
这应该说明：
scala> val hello = Array('h','e','l','l','o',' ','w','o','r','l','d')
hello: Array[Char] = Array(h, e, l, l, o, , w, o, r, l, d)
scala> hello.startsWith("hello")
res9: Boolean = true
这篇关于语义startsWith的阵列的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！