Kotlin:什么是kotlin.String！类型 [英] Kotlin: What is kotlin.String! type

问题描述

我是Kotlin的新手.您能解释一下"kotlin.String"是什么意思吗?类型以及如何使以下代码进行编译?

I am new to Kotlin. Could you explain me what is the meaning of the "kotlin.String!" type and how could I make the following code to compile?

fun withDefault<A>(computation: () -> A, default: A) =
    try { computation() } catch (e: Exception) { default }

fun getHostname1() = withDefault(InetAddress.getLocalHost().getCanonicalHostName, "localhost")

编译器将显示以下消息:

The compiler prints the following message:

Kotlin: Type inference failed: fun <A> withDefault(computation: () -> A, default: A): A
cannot be applied to
(kotlin.String!,kotlin.String)

谢谢.

推荐答案

当类型以!结尾时，表示这是平台类型，并且编译器不对其强制执行null安全性.您可以在官方博客部分Platform Types.

When the type ends with ! it means that this is a platform type and compiler does not enforce null-safety for it. You can read about platform types in official blog, section Platform Types.

我建议这样的解决方法:

I suggest such fix:

fun getHostname1() = withDefault({ InetAddress.getLocalHost().getCanonicalHostName() } , "localhost")

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