Scala - 新的 vs 对象扩展 [英] Scala - new vs object extends

问题描述

使用 new 运算符定义对象与通过扩展类定义独立对象之间有什么区别?

What is the difference between defining an object using the new operator vs defining a standalone object by extending the class?

更具体地说，给定类型 class GenericType { ... }，val a = new GenericType 和 object a extends GenericType<有什么区别?/代码>?

More specifically, given the type class GenericType { ... }, what is the difference between val a = new GenericType and object a extends GenericType?

推荐答案

实际上，object 声明的初始化机制与字节码中的 new 相同.但是，有很多不同之处:

As a practical matter, object declarations are initialized with the same mechanism as new in the bytecode. However, there are quite a few differences:

• object 作为单例——每个都属于一个只有一个实例存在的类；
• object 被延迟初始化——它们只会在第一次被引用时被创建/初始化；
• 一个object和一个class(或trait)同名是同伴;
• 在 object 上定义的方法在伴随的 class 上生成静态转发器；
• object 的成员可以访问伴随 class 的私有成员；
• 在搜索隐式时，相关*类或特征的伴随对象会被调查.

• object as singletons -- each belongs to a class of which only one instance exists;
• object is lazily initialized -- they'll only be created/initialized when first referred to;
• an object and a class (or trait) of the same name are companions;
• methods defined on object generate static forwarders on the companion class;
• members of the object can access private members of the companion class;
• when searching for implicits, companion objects of relevant* classes or traits are looked into.

这些只是我能想到的蝙蝠右侧的一些差异.可能还有其他人.

These are just some of the differences that I can think of right of the bat. There are probably others.

* 什么是相关"的类或特征是一个较长的故事——如果您感兴趣，可以在 Stack Overflow 上查找解释它的问题.如果找不到 scala 标签，请查看 wiki.

* What are the "relevant" classes or traits is a longer story -- look up questions on Stack Overflow that explain it if you are interested. Look at the wiki for the scala tag if you have trouble finding them.

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