什么是Scala惯用语：特质TraitA扩展TraitB或特质TraitA {self：TraitB => }

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问题描述

除了继承方面，以下类模板之间是否存在差异：

Apart from the inheritance aspect, is there a difference between the following class templates:

1| trait TraitA extends TraitB

2| trait TraitA { self: TraitB => }

我想在 TraitA 和 TraitB 但前者在没有后者的情况下无法运作。

I would like to split responsibilities between TraitA and TraitB but the former cannot function without the latter.

您如何表达此意图？对我而言，解决方案[2]将是更自然的方法。但是我不想把实施者的负担混合在一起需要混合的东西。

How would you express this intent? To me solution [2] would be the more natural approach. However I do not want to put the burden on implementers mixing in what needs to be mixed in anyway.

`推荐答案`

我的偏好一般[1]因为，正如你所说的那样，实现者没有负担混合（子类型） TraitB 。如果由于某种原因，希望不继承 TraitB 中的具体实现并强制实现者创建一个在 TraitB 的子类型中进行选择。尽管如此，[1]同样灵活。

My preference is generally [1] because, as you say, the implementor is not burdened to mix in (a sub-type of) TraitB. Perhaps [2] is preferable if, for some reason, it is desirable not to inherit the concrete implementations in TraitB and force the implementor to make a choice among sub-types of TraitB. Still, [1] is just as flexible.

我倾向于仅在必要时使用[2]，例如当类型不是已知的类或特征时，

I tend to use [2] only where necessary, such as when the type isn't a known class or trait,

// Here, Matrix cannot extend type parameter Repr
trait Matrix[+Repr <: Matrix[Repr]] { self: Repr =>
  ...
}

更新。这是另一个小的差异，

Update. Here's another minor difference,

trait B
trait A { self: B => }
def g(ab: A): B = ab // Type mismatch: found A, required B

可选限制无法使用 A 作为 B ，即使该类型已合并。

It's an optional restriction not to be able to use A as a B, even though the type is incorporated.

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TraitB