在 Scala 中，有没有办法检查实例是否是单例对象? [英] In scala, is there any way to check if an instance is a singleton object or not?

问题描述

如果我有一个对象的实例，有没有办法检查我是否有一个单例对象而不是一个类的实例?有什么方法可以做到这一点吗?可能是一些反射API?我知道一个区别是单例对象的类名以 $ 结尾，但这不是一种严格的方式.

If I have an instance of an object, is there a way to check if I have a singleton object rather than an instance of a class? Is there any method can do this? May be some reflection API? I know that one difference is that the class name of a singleton object ends with a $, but this is not a strict way.

推荐答案

是的，使用文档很少的 scala.Singleton 类型:

Yep, using the little-documented scala.Singleton type:

def isSingleton[A](a: A)(implicit ev: A <:< Singleton = null) = 
  Option(ev).isDefined

然后:

scala> val X = new Foo(10)
X: Foo = Foo@3d5c818f

scala> object Y extends Foo(11)
defined object Y

scala> isSingleton(X)
res0: Boolean = false

scala> isSingleton(Y)
res1: Boolean = true

我的 isSingleton 方法只是一个演示，它提供了一个运行时布尔值，该值告诉您表达式是否静态类型为单例类型，但您也可以使用 Singleton 作为编译时类型是单例类型的证据.

My isSingleton method is just a demonstration that provides a runtime boolean value that tells you whether or not an expression is statically typed as a singleton type, but you can also use Singleton as evidence at compile time that a type is a singleton type.

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