++: 运算符对列表有什么作用? [英] What does the ++: operator do to a list?

问题描述

好吧，Scala 让我感觉很密集.我发现这些文档非常难以理解——更糟糕的是，你不能用谷歌搜索Scala ++:"这个词，因为谷歌放弃了运营商术语！

Alright, Scala has me feeling pretty dense. I'm finding the docs pretty impenetrable -- and worse, you can't Google the term "Scala ++:" because Google drops the operator terms!

我正在阅读一些代码并看到这一行:

I was reading some code and saw this line:

Seq(file) ++: children.flatMap(walkTree(_))  

但是想不通.Seq 的文档显示了三件事:

But couldn't figure it out. The docs for Seq show three things:

++
++:
++:  

后两者超负荷做..某事.文档中的实际解释说它们与 ++ 做同样的事情.即，将一个列表添加到另一个列表.

Where the latter two are over loaded to do.. something. The actual explanation in the doc says that they do the same thing as ++. Namely, add one list to another.

那么，运算符之间到底有什么区别..?

So, what exactly is the difference between the operators..?

推荐答案

++ 和 ++: 当操作数是不同类型的集合时返回不同的结果.++ 返回与左侧相同的集合类型，++: 返回与右侧相同的集合类型:

++ and ++: return different results when the operands are different types of collection. ++ returns the same collection type as the left side, and ++: returns the same collection type as the right side:

scala> List(5) ++ Vector(5)
res2: List[Int] = List(5, 5)

scala> List(5) ++: Vector(5)
res3: scala.collection.immutable.Vector[Int] = Vector(5, 5)

++: 有两个重载版本，只是为了实现的原因.++: 需要能够接受任何TraversableOnce，但是为Traversable(TraversableOnce) 以提高效率.

There are two overloaded versions of ++: solely for implementation reasons. ++: needs to be able to take any TraversableOnce, but an overloaded version is provided for Traversable (a subtype of TraversableOnce) for efficiency.

这篇关于++: 运算符对列表有什么作用?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IT屋！