Enumeration应该算是程序语言里面比较通用的一个类型，在scala中也存在这样的类型， 我们看下Enumeration的定义：
abstract class Enumeration (initial: Int) extends Serializable
Enumeration是一个抽象类，它定义四个value方法，来设置内部的值， 四个value方法如下定义：
/** Creates a fresh value, part of this enumeration. */
protected final def Value: Value = Value(nextId)
/** Creates a fresh value, part of this enumeration, identified by the
* integer `i`.
*
* @param i An integer that identifies this value at run-time. It must be
* unique amongst all values of the enumeration.
* @return Fresh value identified by `i`.
*/
protected final def Value(i: Int): Value = Value(i, nextNameOrNull)
/** Creates a fresh value, part of this enumeration, called `name`.
*
* @param name A human-readable name for that value.
* @return Fresh value called `name`.
*/
protected final def Value(name: String): Value = Value(nextId, name)
/** Creates a fresh value, part of this enumeration, called `name`
* and identified by the integer `i`.
*
* @param i An integer that identifies this value at run-time. It must be
* unique amongst all values of the enumeration.
* @param name A human-readable name for that value.
* @return Fresh value with the provided identifier `i` and name `name`.
*/
protected final def Value(i: Int, name: String): Value = new Val(i, name)
知道如何设置Enum的值后，我们就可以尝试创建一个Enum了。
println("Step 1: How to create an enumeration")
object Donut extends Enumeration {
type Donut = Value
val Glazed = Value("Glazed")
val Strawberry = Value("Strawberry")
val Plain = Value("Plain")
val Vanilla = Value("Vanilla")
}
上面的例子中，我们创建了一个Enum，并且设置了几个值。
下面我们看下怎么取到Enum的值：
println("\nStep 2: How to print the String value of the enumeration")
println(s"Vanilla Donut string value = ")
你可以看到如下的输出：
Step 2: How to print the String value of the enumeration
Vanilla Donut string value = Vanilla
下面是怎么输出Enum的id：
println("\nStep 3: How to print the id of the enumeration")
println(s"Vanilla Donut's id = ")
结果如下：
Step 3: How to print the id of the enumeration
Vanilla Donut's id = 3
怎么输出所有的Enum项呢？
println("\nStep 4: How to print all the values listed in Enumeration")
println(s"Donut types = ")
输出结果如下：
Step 4: How to print all the values listed in Enumeration
Donut types = Donut.ValueSet(Glazed, Strawberry, Plain, Vanilla)
接下来，我们看下怎么打印出所有的Enum：
println("\nStep 5: How to pattern match on enumeration values")
Donut.values.foreach {
case d if (d == Donut.Strawberry || d == Donut.Glazed) => println(s"Found favourite donut = $d")
case _ => None
}
输出如下：
Step 5: How to pattern match on enumeration values
Found favourite donut = Glazed
Found favourite donut = Strawberry
最后，我们看下怎么改变Enum值的顺序：
println("\nStep 6: How to change the default ordering of enumeration values")
object DonutTaste extends Enumeration{
type DonutTaste = Value
val Tasty = Value(0, "Tasty")
val VeryTasty = Value(1, "Very Tasty")
val Ok = Value(-1, "Ok")
}
println(s"Donut taste values = ")
println(s"Donut taste of OK id = ")
输出结果如下：
Step 6: How to change the default ordering of enumeration values
Donut taste values = DonutTaste.ValueSet(Ok, Tasty, Very Tasty)
Donut taste of OK id = -1
