【scala初学】可变集合和不可变集合

妖狐艹你老母 2022-05-22 13:13 255阅读 0赞

scala的集合系统的区分了可变（ mutable  ）和不可变（immutable ）集合。一个mutable  集合能够更新甚至扩展空间，这意味着你能改变，增加，或者删除一个集合的元素。 一个immutable集合，刚好相反，不能改变。你仍然可以做一些类似的增加，删除，或者更新，但是实际上（书生：跟java的string一样）他返回了一个新的对象，这里面就是指返回了一个新的集合，而老的集合没有改变。

所有的集合类在`scala.collection` 包中，或者他的子包中，分为mutable，immutable以及generic 。 大部分集合都有三个同名的类（经验翻译，不同见解可以指正）,每个同名类有不同的特征.

scala.collection.immutable包中元素不可变，可以保证你在任何时间访问他时元素值都是相同的

scala.collection.mutabl 包中的元素可变，所以你要知道他在何时何地变化了

有一些集合类不在上述两个包下，如[collection.IndexedSeq\[T\]][collection.IndexedSeq_T] 是[collection.immutable.IndexedSeq\[T\]][collection.immutable.IndexedSeq_T] 和[collection.mutable.IndexedSeq\[T\]][collection.mutable.IndexedSeq_T] 的父类。一般情况下会在collection包下定义接口，由mutable和immutable两个包实现。

跳过一段废话。

（书生：重点）

scala默认的集合包是不可变的 ，即cala.collection.immutable。 举例：

`Set` 如果没有导入，默认collection.immutable.Set

如果你想用一个可变的Set，你需要导入collection.mutable.Set，即：

如果想两个都引用，又想简单写，有个办法：

直接用Set则仍是默认不可变的，如果想Set是mutable的，写成mutable.Set

还有一个包  `collection.generic。 该package包含了实现集合的构建块。典型的， generic里classes推迟实现一些函数。另一方面，集合framework的用户需要在一些特殊环境中用到generic中的类。`

为了便利，以及向后兼容，一些重要的类型有别名，因此你能用它们的简称，而不需要import.如List

其他的类型别名有[Traversable][], [Iterable][], [Seq][], [IndexedSeq][collection.IndexedSeq_T], [Iterator][], [Stream][], [Vector][],[StringBuilder][], and [Range][].

下图展示了最高等级的抽象类 abstract classes 或者接口 traits

![collections.png][]

下图展示 `scala.collection.immutable`.

![collections.immutable.png][]

下图展示 `scala.collection.mutable`.

![collections.mutable.png][]

一些例子，父类和实现类，参考上图：

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    <div style="max-width:100%;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Traversable(</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">1</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">2</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">3</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">)</code> 
     </div> 
     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Iterable(</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#0000FF;">"x"</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#0000FF;">"y"</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#0000FF;">"z"</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">)</code> 
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     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Map(</code> 
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      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">-&gt;&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">24</code> 
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      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#0000FF;">"y"</code>&nbsp; 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">-&gt;&nbsp;</code> 
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      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Set(Color.red,&nbsp;Color.green,&nbsp;Color.blue)</code> 
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     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">SortedSet(</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#0000FF;">"hello"</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#0000FF;">"world"</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">)</code> 
     </div> 
     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Buffer(x,&nbsp;y,&nbsp;z)</code> 
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     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">IndexedSeq(</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">1.0</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">2.0</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">)</code> 
     </div> 
     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">LinearSeq(a,&nbsp;b,&nbsp;c)</code> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

以上toString方法实现相同，并且写法与如上相同。

所有集合类都支持Traversable提供的API，但只有一些特殊类有意义。如`Traversable` 类中的 map 方法返回另一个`Traversable` ，但结果类型会在子类中被重写。例如，在List中调用map，会返回一个List结果，在Set中调用返回Set.

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      1 
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    <div style="max-width:100%;margin:0px;padding:0px .5em 0px 1em;font-size:1em;background-image:none;border-width:0px 3px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;line-height:1.1em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;">
      2 
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    <div style="max-width:100%;margin:0px;padding:0px .5em 0px 1em;font-size:1em;background-image:none;border-width:0px 3px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;line-height:1.1em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;">
      3 
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    <div style="max-width:100%;margin:0px;padding:0px .5em 0px 1em;font-size:1em;background-image:none;border-width:0px 3px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);float:none;line-height:1.1em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;">
      4 
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   <td style="max-width:748px;width:728px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;border-width:0px;font-size:1em;background:none;float:none;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
    <div style="max-width:100%;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">scala&gt;&nbsp;List(</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">1</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">2</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">3</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">)&nbsp;map&nbsp;(</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">_</code>&nbsp; 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">+&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">1</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">)&nbsp;</code> 
     </div> 
     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">res</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">0</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">:</code>&nbsp; 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">List[Int]&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">=</code>&nbsp; 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">List(</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">2</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">3</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">4</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">)</code> 
     </div> 
     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">scala&gt;&nbsp;Set(</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">1</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">2</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">3</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">)&nbsp;map&nbsp;(</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">_</code>&nbsp; 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">*&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">2</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">)</code> 
     </div> 
     <div style="max-width:100%;white-space:nowrap;margin:0px;padding:0px 1em;font-size:1em;background-image:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;"> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">res</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">0</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">:</code>&nbsp; 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Set[Int]&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">=</code>&nbsp; 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Set(</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">2</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">4</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">,&nbsp;</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">6</code> 
      <code style="max-width:100%;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;margin:0px;padding:0px;font-size:1em;background:none;border:0px;float:none;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">)</code> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

上述集合函数库中的实现方式被成为 uniform return type principle. -- 一致返回类型原则

集合的大部分存在（指名字相同的类分别存在）三个包中：root,mutable,immutable.只有Buffer trait,只存在mutable集合中

[collection.IndexedSeq_T]: http://www.scala-lang.org/api/current/scala/collection/IndexedSeq.html
[collection.immutable.IndexedSeq_T]: http://www.scala-lang.org/api/current/scala/collection/immutable/IndexedSeq.html
[collection.mutable.IndexedSeq_T]: http://www.scala-lang.org/api/current/scala/collection/mutable/IndexedSeq.html
[Traversable]: http://www.scala-lang.org/api/current/scala/collection/Traversable.html
[Iterable]: http://www.scala-lang.org/api/current/scala/collection/Iterable.html
[Seq]: http://www.scala-lang.org/api/current/scala/collection/Seq.html
[Iterator]: http://www.scala-lang.org/api/current/scala/collection/Iterator.html
[Stream]: http://www.scala-lang.org/api/current/scala/collection/immutable/Stream.html
[Vector]: http://www.scala-lang.org/api/current/scala/collection/immutable/Vector.html
[StringBuilder]: http://www.scala-lang.org/api/current/scala/collection/mutable/StringBuilder.html
[Range]: http://www.scala-lang.org/api/current/scala/collection/immutable/Range.html
[collections.png]: /images/20220522/cb791d3d2d0e4440b2cfcfabe1ea9b8f.png
[collections.immutable.png]: /images/20220522/7f94d15e275247f5a617a7487324ac76.png
[collections.mutable.png]: /images/20220522/591e0ec29b93444fb2fc833f4b35ded0.png