什么取代了 Scala 中的类变量？
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What replaces class variables in scala?
提问by paradigmatic
In Java I sometimes use class variables to assign a unique ID to each new instance. I do something like
在 Java 中，我有时使用类变量为每个新实例分配一个唯一的 ID。我做类似的事情
public class Foo {
private static long nextId = 0;
public final long id;
public Foo() {
id = nextId;
nextId++;
}
[...]
}
How can I do this in Scala?
我怎样才能在 Scala 中做到这一点？
回答by Thomas Jung
Variables on the companion object:
伴随对象上的变量：
object Foo{
private var current = 0
private def inc = {current += 1; current}
}
class Foo{
val i = Foo.inc
println(i)
}
回答by Carl Smotricz
To amplify on Thomas' answer:
放大托马斯的回答：
The objectdefinition is usually put in the same file with the class, and musthave the same name. This results in a single instance of an object having the name of the class, which contains whatever fields you define for it.
该object定义通常被放在与类相同的文件，并且必须具有相同的名称。这会产生一个具有类名称的对象的单个实例，其中包含您为它定义的任何字段。
A handy do-it-yourself Singleton construction kit, in other words.
换句话说，这是一个方便的自己动手做的 Singleton 构建套件。
At the JVM level, the object definition actually results in the definition of a new class; I think it's the same name with a $appended, e.g. Foo$. Just in case you have to interoperate some of this stuff with Java.
在JVM层面，对象定义实际上导致了一个新类的定义；我认为它与$附加的名称相同，例如Foo$. 以防万一您必须与 Java 互操作这些东西。
