为什么分配不是陈述 [英] why assignments are not statements

问题描述

我有以下代码:

class Presenter {
    private var view : View? = null

    fun attachView(view: View) = this.view = view // error: Assignment is not a statement

    fun detachView() = view = null // error: Assignment is not a statement
}

我知道我会写:

class Presenter {
    var view : View? = null
}

和随后的代码中，只需调用presenter.view = View()和presenter.view = null而不是attachView/detachView.但是我认为这不太可读.

and later in code just call presenter.view = View() and presenter.view = null instead of attachView/detachView. But I think this is much less readable.

那么为什么我不能在Kotlin中将赋值用作表达式主体?为什么赋值不只是类型为Unit的语句?

So why can't I use assignments as expression bodies in Kotlin? Why isn't assignment just a statement of type Unit?

推荐答案

我们是否喜欢它，这仅仅是语言创建者做出的设计决定.有关更多详细信息，请参见此讨论:

Whether we like it or not, this was simply a design decision which the language creators made. See this discussion for more details:

https://discuss.kotlinlang.org /t/assignment-not-allow-in-while-expression/339

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