安全类型转换与可空值转换 [英] Safe cast vs cast to nullable

问题描述

两者之间有什么区别

x as? String

和

x as String?

它们似乎都产生一个String?类型. 科特琳页面不能为我回答.

They both seem to produce a String? type. The Kotlin page doesn't answer it for me.

更新:

为了澄清，我的问题是:

To clarify, my question is:

完全具有as?运算符的目的是什么，因为对于任何对象x和任何类型T，表达式(c4>都可以(我认为)改写为x as T?吗? /p>

What is the purpose of having an as? operator at all, since for any object x and for any type T, the expression x as? T can be (I think) rephrased as x as T? ?

推荐答案

区别在于x是其他类型时:

The difference lies in when x is a different type:

val x: Int = 1

x as String? // Causes ClassCastException, cannot assign Int to String?

x as? String // Returns null, since x is not a String type.

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