list 将项目添加到不可变的 Seq
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/8295597/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Adding an item to an immutable Seq
提问by Nikita Volkov
Say, I have a sequence of strings as an input and I want to get a new immutable Seqwhich consists of elements of the input and an item "c". Here are two methods that I've discovered to be working:
说，我有一个字符串序列作为输入，我想获得一个新的不可变Seq元素，它由 input 元素和 item 组成"c"。以下是我发现有效的两种方法：
assert(Seq("a", "b", "c") == Seq("a", "b") ++ Seq("c"))- the problem with this one is that it seems that instantiating a temporary sequence (Seq("c")) just for the sake of the operation is rendundant and will result in overheadassert(Seq("a", "b", "c") == List("a", "b") ::: "c" :: Nil)- this one restricts the type of input collection to be aList, soSeq("a", "b") ::: "c" :: Nilwon't work. Also it seems that instantiating aNilmay aswell result in overhead
assert(Seq("a", "b", "c") == Seq("a", "b") ++ Seq("c"))- 这个的问题是，Seq("c")为了操作而实例化一个临时序列 ( )似乎是多余的，会导致开销assert(Seq("a", "b", "c") == List("a", "b") ::: "c" :: Nil)- 这将输入集合的类型限制为 aList，因此Seq("a", "b") ::: "c" :: Nil不起作用。似乎实例化 aNil也可能导致开销
My questions are:
我的问题是：
- Is there any other way of performing this operation?
- Which one is better?
- Isn't
Seq("a", "b") ::: Nilnot being allowed a flaw of Scala's developers?
- 有没有其他方法可以执行此操作？
- 哪一个更好？
- 是不是
Seq("a", "b") ::: Nil没有被允许Scala的开发商缺陷？
回答by Ben James
Use the :+(append) operator to create a newSequsing:
使用:+(append) 运算符创建一个新的Seq使用：
val seq = Seq("a", "b") :+ "c"
// seq is now ("a","b","c")
Note: :+will create a new Seqobject.
If you have
注意：:+将创建一个新Seq对象。如果你有
val mySeq = Seq("a","b")
and you will call
你会打电话
mySeq :+ "c"
mySeqwill still be ("a","b")
mySeq仍然会 ("a","b")
Note that some implementations of Seqare more suitable for appending than others. Listis optimised for prepending. Vectorhas fast append and prepend operations.
请注意， 的某些实现Seq比其他实现更适合附加。List针对前置进行了优化。Vector具有快速追加和前置操作。
:::is a method on Listwhich requires another Listas its parameter - what are the advantages that you see in it accepting other types of sequence? It would have to convert other types to a List. If you know that Listis efficient for your use case then use :::(if you must). If you want polymorphic behaviour then use the generic ++.
:::是一种List需要另一个List作为其参数的方法 - 您在它接受其他类型的序列时看到的优势是什么？它必须将其他类型转换为List. 如果您知道这List对您的用例有效，则使用:::（如果必须）。如果您想要多态行为，请使用泛型++.
There's no instantiation overhead to using Nil; you don't instantiate it because it's a singleton.
使用没有实例化开销Nil；你不实例化它，因为它是一个单身人士。
