Scala supports single inheritance, not multiple inheritance.
Scala支持单继承，不支持多继承。
That's because objects in the real world just don't fit into a simple single inheritance hierarchy.
那是因为实际世界中的对象不会刚好适合一个简单的单继承层次结构。
Objective-C only supports single inheritance between classes, while UML supports multiple inheritances.
Objective - C只支持类之间的单一继承，而UML支持多重继承。
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