在 Scala 中拥有伴生对象的基本原理是什么? [英] What is the rationale behind having companion objects in Scala?

问题描述

是否有需要类的伴生对象(单例)的情况?为什么我要创建一个类，比如 Foo 并为它创建一个伴生对象?

Is there a case where a companion object (singleton) for a class is needed? Why would I want to create a class, say Foo and also create a companion object for it?

推荐答案

伴随对象基本上提供了一个可以放置类静态"方法的地方.此外，伴生对象或伴生模块可以完全访问类成员，包括私有成员.

The companion object basically provides a place where one can put "static-like" methods. Furthermore, a companion object, or companion module, has full access to the class members, including private ones.

伴随对象非常适合封装工厂方法之类的东西.例如，不必到处都有 Foo 和 FooFactory，您可以让一个带有伴随对象的类承担工厂职责.

Companion objects are great for encapsulating things like factory methods. Instead of having to have, for example, Foo and FooFactory everywhere, you can have a class with a companion object take on the factory responsibilities.

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