Question

我想写这样的东西：

/**
 * Represents a state, large or small.
 */
interface State {
    /**
     * 
     */
    val changeValue: StateChange<This> // does not compile; "This" is a keyword I made up that might reference the implementing class
}


/**
 * Represents a change in a state, large or small.
 *
 * @param StateType The type of state that has changed
 */
interface StateChange<StateType: State>

但是，正如我的评论所述，我不知道这个的语法。这是存在吗？或者我是否必须使用变通方法，例如强制State将其作为通用参数？

如果不明显，我无法使用val changeValue: StateChange<State>，因为这样就可以了，我不想要这样做：

// BAD EXAMPLE - This is what I want to avoid
class Foo: State { val changeValue: StateChange<Bar> = Bar().changeValue }
class Bar: State { val changeValue: StateChange<Foo> = Foo().changeValue }

Answer 1

您可以使用具有递归上限的类：

interface State<T : State<T>> {
    val changeValue: StateChange<T>
}

interface StateChange<StateType: State<StateType>>

现在这段代码将不再编译：

class Foo: State<Foo> { val changeValue: StateChange<Bar> = Bar().changeValue }
class Bar: State<Bar> { val changeValue: StateChange<Foo> = Foo().changeValue }

Kotlin是否允许函数返回此接口的实现类型的值？

1 个答案: