blocks|key|1470624|text|http://www.scala-lang.org/docu/files/api/scala/Enumeration.html|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1470625|示例用法|1470626|++object+Main+extends+App+{

++++object+WeekDay+extends+Enumeration+{
++++++type+WeekDay+=+Value
++++++val+Mon,+Tue,+Wed,+Thu,+Fri,+Sat,+Sun+=+Value
++++}
++++import+WeekDay._

++++def+isWorkingDay(d:+WeekDay)+=+!+(d+==+Sat+%7C%7C+d+==+Sun)

++++WeekDay.values+filter+isWorkingDay+foreach+println
++}|code-block|syntax|javascript|1470627|entityMap|0|LINK|mutability|MUTABLE|url^0|0|1R|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@$A|S|B|T|1|U]]|C|$]]|$1|D|3|E|5|6|7|V|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|W|8|@]|9|@]|C|$I|J]]|$1|K|3|-4|5|6|7|X|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|4]]]]

<a href="http://www.scala-lang.org/docu/files/api/scala/Enumeration.html" rel="noreferrer">http://www.scala-lang.org/docu/files/api/scala/Enumeration.html</a>

Example use

<pre><code> object Main extends App {

 object WeekDay extends Enumeration {
 type WeekDay = Value
 val Mon, Tue, Wed, Thu, Fri, Sat, Sun = Value
 }
 import WeekDay._

 def isWorkingDay(d: WeekDay) = ! (d == Sat || d == Sun)

 WeekDay.values filter isWorkingDay foreach println
 }
</code></pre>

blocks|key|1255983|text|声明命名枚举的一种不太冗长的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1255984|object+WeekDay+extends+Enumeration("Sun",+"Mon",+"Tue",+"Wed",+"Thu",+"Fri",+"Sat")+{
++type+WeekDay+=+Value
++val+Sun,+Mon,+Tue,+Wed,+Thu,+Fri,+Sat+=+Value
}

WeekDay.valueOf("Wed")+//+returns+Some(Wed)
WeekDay.Fri.toString+++//+returns+Fri|code-block|syntax|javascript|1255985|当然，这里的问题是，您需要保持名称和val的顺序同步，如果name和val在同一行中声明，则更容易做到这一点。|1255986|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

A slightly less verbose way of declaring named enumerations:

<pre><code>object WeekDay extends Enumeration("Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat") {
 type WeekDay = Value
 val Sun, Mon, Tue, Wed, Thu, Fri, Sat = Value
}

WeekDay.valueOf("Wed") // returns Some(Wed)
WeekDay.Fri.toString // returns Fri
</code></pre>

Of course the problem here is that you will need to keep the ordering of the names and vals in sync which is easier to do if name and val are declared on the same line.

blocks|key|1256038|text|您可以使用密封的抽象类来代替枚举，例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1256039|sealed+abstract+class+Constraint(val+name:+String,+val+verifier:+Int+=>+Boolean)

case+object+NotTooBig+extends+Constraint("NotTooBig",+(_+<+1000))
case+object+NonZero+extends+Constraint("NonZero",+(_+!=+0))
case+class+NotEquals(x:+Int)+extends+Constraint("NotEquals+"+%2B+x,+(_+!=+x))

object+Main+{

++def+eval(ctrs:+Seq[Constraint])(x:+Int):+Boolean+=
++++(true+/:+ctrs){+case+(accum,+ctr)+=>+accum+&&+ctr.verifier(x)+}

++def+main(args:+Array[String])+{
++++val+ctrs+=+NotTooBig+::+NotEquals(5)+::+Nil
++++val+evaluate+=+eval(ctrs)+_

++++println(evaluate(3000))
++++println(evaluate(3))
++++println(evaluate(5))
++}

}|code-block|syntax|javascript|1256040|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can use a sealed abstract class instead of the enumeration, for example:

<pre><code>sealed abstract class Constraint(val name: String, val verifier: Int =&gt; Boolean)

case object NotTooBig extends Constraint("NotTooBig", (_ &lt; 1000))
case object NonZero extends Constraint("NonZero", (_ != 0))
case class NotEquals(x: Int) extends Constraint("NotEquals " + x, (_ != x))

object Main {

 def eval(ctrs: Seq[Constraint])(x: Int): Boolean =
 (true /: ctrs){ case (accum, ctr) =&gt; accum &amp;&amp; ctr.verifier(x) }

 def main(args: Array[String]) {
 val ctrs = NotTooBig :: NotEquals(5) :: Nil
 val evaluate = eval(ctrs) _

 println(evaluate(3000))
 println(evaluate(3))
 println(evaluate(5))
 }

}
</code></pre>

blocks|key|1256224|text|在对Scala中“枚举”的所有选项进行了广泛的研究之后，我在另一个StackOverflow+thread上发布了关于这个领域的更完整的概述。它包括对“密封特征%2B案例对象”模式的解决方案，在该模式中我解决了JVM类/对象初始化排序问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1256225|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/25923651/501113^0|X|K|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

After doing extensive research on all the options around "enumerations" in Scala, I posted a much more complete overview of this domain on another <a href="https://stackoverflow.com/a/25923651/501113">StackOverflow thread</a>. It includes a solution to the "sealed trait + case object" pattern where I have solved the JVM class/object initialization ordering problem.

blocks|key|1256255|text|刚刚发现了enumeratum。这是相当令人惊叹的，也是同样令人惊叹的，这并不是很广为人知！|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1256256|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/lloydmeta/enumeratum^0|5|A|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

just discovered <a href="https://github.com/lloydmeta/enumeratum" rel="noreferrer">enumeratum</a>. it's pretty amazing and equally amazing it's not more well known!

blocks|key|1470980|text|Dotty+(Scala+3)将支持原生枚举。检查here和here。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1470981|entityMap|0|LINK|mutability|MUTABLE|url|https://dotty.epfl.ch/docs/reference/enums/enums.html|1|https://github.com/lampepfl/dotty/issues/1970^0|P|4|0|U|4|1|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]|$A|R|B|S|1|T]]|C|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]]]

Dotty (Scala 3) will have native enums supported. Check <a href="https://dotty.epfl.ch/docs/reference/enums/enums.html" rel="nofollow noreferrer">here</a> and <a href="https://github.com/lampepfl/dotty/issues/1970" rel="nofollow noreferrer">here</a>.

blocks|key|1471018|text|在Scala中，使用https://github.com/lloydmeta/enumeratum非常方便。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1471019|该项目非常适合使用示例和文档|1471020|他们的文档中的这个例子应该会让你感兴趣|1471021|import+enumeratum._

sealed+trait+Greeting+extends+EnumEntry

object+Greeting+extends+Enum[Greeting]+{

++/*
+++`findValues`+is+a+protected+method+that+invokes+a+macro+to+find+all+`Greeting`+object+declarations+inside+an+`Enum`

+++You+use+it+to+implement+the+`val+values`+member
++*/
++val+values+=+findValues

++case+object+Hello+++extends+Greeting
++case+object+GoodBye+extends+Greeting
++case+object+Hi++++++extends+Greeting
++case+object+Bye+++++extends+Greeting

}

//+Object+Greeting+has+a+`withName(name:+String)`+method
Greeting.withName("Hello")
//+=>+res0:+Greeting+=+Hello

Greeting.withName("Haro")
//+=>+java.lang.IllegalArgumentException:+Haro+is+not+a+member+of+Enum+(Hello,+GoodBye,+Hi,+Bye)

//+A+safer+alternative+would+be+to+use+`withNameOption(name:+String)`+method+which+returns+an+Option[Greeting]
Greeting.withNameOption("Hello")
//+=>+res1:+Option[Greeting]+=+Some(Hello)

Greeting.withNameOption("Haro")
//+=>+res2:+Option[Greeting]+=+None

//+It+is+also+possible+to+use+strings+case+insensitively
Greeting.withNameInsensitive("HeLLo")
//+=>+res3:+Greeting+=+Hello

Greeting.withNameInsensitiveOption("HeLLo")
//+=>+res4:+Option[Greeting]+=+Some(Hello)

//+Uppercase-only+strings+may+also+be+used
Greeting.withNameUppercaseOnly("HELLO")
//+=>+res5:+Greeting+=+Hello

Greeting.withNameUppercaseOnlyOption("HeLLo")
//+=>+res6:+Option[Greeting]+=+None

//+Similarly,+lowercase-only+strings+may+also+be+used
Greeting.withNameLowercaseOnly("hello")
//+=>+res7:+Greeting+=+Hello

Greeting.withNameLowercaseOnlyOption("hello")
//+=>+res8:+Option[Greeting]+=+Some(Hello)|code-block|syntax|javascript|1471022|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/lloydmeta/enumeratum^0|A|13|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|C|$K|L]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

In Scala it is very comfortable with <a href="https://github.com/lloydmeta/enumeratum" rel="nofollow noreferrer">https://github.com/lloydmeta/enumeratum</a>

Project is really good with examples and documentation

Just this example from their docs should makes you interested in

<pre><code>import enumeratum._

sealed trait Greeting extends EnumEntry

object Greeting extends Enum[Greeting] {

 /*
 `findValues` is a protected method that invokes a macro to find all `Greeting` object declarations inside an `Enum`

 You use it to implement the `val values` member
 */
 val values = findValues

 case object Hello extends Greeting
 case object GoodBye extends Greeting
 case object Hi extends Greeting
 case object Bye extends Greeting

}

// Object Greeting has a `withName(name: String)` method
Greeting.withName("Hello")
// =&gt; res0: Greeting = Hello

Greeting.withName("Haro")
// =&gt; java.lang.IllegalArgumentException: Haro is not a member of Enum (Hello, GoodBye, Hi, Bye)

// A safer alternative would be to use `withNameOption(name: String)` method which returns an Option[Greeting]
Greeting.withNameOption("Hello")
// =&gt; res1: Option[Greeting] = Some(Hello)

Greeting.withNameOption("Haro")
// =&gt; res2: Option[Greeting] = None

// It is also possible to use strings case insensitively
Greeting.withNameInsensitive("HeLLo")
// =&gt; res3: Greeting = Hello

Greeting.withNameInsensitiveOption("HeLLo")
// =&gt; res4: Option[Greeting] = Some(Hello)

// Uppercase-only strings may also be used
Greeting.withNameUppercaseOnly("HELLO")
// =&gt; res5: Greeting = Hello

Greeting.withNameUppercaseOnlyOption("HeLLo")
// =&gt; res6: Option[Greeting] = None

// Similarly, lowercase-only strings may also be used
Greeting.withNameLowercaseOnly("hello")
// =&gt; res7: Greeting = Hello

Greeting.withNameLowercaseOnlyOption("hello")
// =&gt; res8: Option[Greeting] = Some(Hello)
</code></pre>

blocks|key|1471072|text|从Scala3开始，现在有了enum+keyword，它可以表示一组常量(和其他用例)|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1471073|enum+Color:
+++case+Red,+Green,+Blue

scala>+val+red+=+Color.Red
val+red:+Color+=+Red
scala>+red.ordinal
val+res0:+Int+=+0|code-block|syntax|javascript|1471074|entityMap|0|LINK|mutability|MUTABLE|url|https://dotty.epfl.ch/docs/reference/enums/enums.html^0|E|C|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Starting from Scala 3, there is now <a href="https://dotty.epfl.ch/docs/reference/enums/enums.html" rel="nofollow noreferrer">enum keyword</a> which can represent a set of constants (and other use cases)
<pre><code>enum Color:
 case Red, Green, Blue

scala&gt; val red = Color.Red
val red: Color = Red
scala&gt; red.ordinal
val res0: Int = 0
</code></pre>

Scala doesn't have type-safe <code>enum</code>s like Java has. Given a set of related constants, what would be the best way in Scala to represent those constants?

How to model type-safe enum types?

Java

Scala没有像Java那样的类型安全enum。给定一组相关常量，在Scala中表示这些常量的最佳方式是什么？

问如何对类型安全的枚举类型建模？
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