当类层次结构中存在原始类型时，为什么Scala会抱怨非法继承？ [英] Why does Scala complain about illegal inheritance when there are raw types in the class hierarchy?

问题描述

我正在编写一个包含Scala的包装器 ObservableBuffer 并触发与 Eclipse / JFace数据绑定框架。

I'm writing a wrapper that takes a Scala ObservableBuffer and fires events compatible with the Eclipse/JFace Databinding framework.

在数据绑定框架中，有一个抽象 <$ c装饰普通Java列表的$ c> ObservableList 。我想重用这个基类，但即使这个简单的代码也会失败：

In the Databinding framework, there is an abstract ObservableList that decorates a normal Java list. I wanted to reuse this base class, but even this simple code fails:

val list = new java.util.ArrayList[Int]
val obsList = new ObservableList(list, null) {}

有错误：

illegal inheritance; anonymous class $anon inherits different type instances of trait Collection: java.util.Collection[E] and java.util.Collection[E]
illegal inheritance; anonymous class $anon inherits different type instances of trait Iterable: java.lang.Iterable[E] and java.lang.Iterable[E]

为什么？它与原始类型有关吗？ ObservableList 实现 IObservableList ，它扩展了原始类型 java.util.List 。这是预期的行为，我该如何解决它？

Why? Does it have to do with raw types? ObservableList implements IObservableList, which extends the raw type java.util.List. Is this expected behavior, and how can I work around it?

推荐答案

在继承层次结构中使用Java原始类型会导致这种情况问题。一种解决方案是编写一小部分Java来修复原始类型，如 Scala类无法覆盖扩展java.util.comparator的Java接口的比较方法

Having a Java raw type in the inheritance hierarchy causes this kind of problem. One solution is to write a tiny bit of Java to fix up the raw type as in the answer for Scala class cant override compare method from Java Interface which extends java.util.comparator

有关原因类型为scala存在问题的原因，请参阅 http：//lampsvn.epfl .ch / trac / scala / ticket / 1737 。该bug有一个解决方法，使用可能不适用于这种特定情况的存在类型，至少在没有大量转换的情况下，因为java.util.List类型参数在co和contra变体位置。

For more about why raw types are problematic for scala see this bug http://lampsvn.epfl.ch/trac/scala/ticket/1737 . That bug has a workaround using existential types that probably won't work for this particular case, at least not without a lot of casting, because the java.util.List type parameter is in both co and contra variant positions.

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