为什么自类型类可以声明类 [英] why self-type class can declare class

问题描述

我知道 Scala 只能混合特征，这对依赖注入和蛋糕模式很有意义.我的问题是为什么我仍然可以声明一个需要另一个类"但不需要特征的类.

I know Scala can only mixin traits, it makes sense for dependency injection and cake pattern. My question is why I can still declare a class which need another "class" but not trait.

代码:

class C
class D { self : C =>}

这个还是编译成功了.我认为它应该编译失败，因为此时如何新建实例 D (C is class not trait).

This is still complied successfully. I thought it should failed compiled, because at this point how can new instance D (C is class not trait).

尝试实例化 D 时:

new D with C//编译失败类C需要是一个trait来混入.

new D with C //compilation fail class C needs to be a trait to be mixed in.

推荐答案

你应该明确地使 class D 成为 extends C 如下:

You should explicitly make class D to extends C as follows:

class C
class D extends C { self: C => }

此外，您可以参考帖子 一个类具有另一个类的 self 类型有意义吗?，这清楚地解释了这个问题.

Furthermore, you can refer to the post Does a class with a self type of another class make sense?, which explains this problem clearly.

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