将可为空的类型转换为其不可为空的类型? [英] Convert a nullable type to its non-nullable type?

问题描述

我有一堆具有空值属性的bean，如下所示:

I have a bunch of beans that have nullable properties like so:

package myapp.mybeans;

data class Foo(val name : String?);

我在全局空间中有一个像这样的方法:

And I have a method in the global space like so:

package myapp.global;

public fun makeNewBar(name : String) : Bar
{
  ...
}

在其他地方，我需要使用Foo内部的内容制作一个Bar.所以，我这样做:

And somewhere else, I need to make a Bar from the stuff that's inside Foo. So, I do this:

package myapp.someplaceElse;

public fun getFoo() : Foo? { }
...
val foo : Foo? = getFoo();

if (foo == null) { ... return; }


// I know foo isn't null and *I know* that foo.name isn't null
// but I understand that the compiler doesn't.
// How do I convert String? to String here? if I do not want
// to change the definition of the parameters makeNewBar takes?
val bar : Bar = makeNewBar(foo.name);

此外，在这里使用foo.name进行一些转换以每次用小东西清理它，而一方面为我提供了编译时保证和安全性，但在大多数情况下这是一个很大的麻烦.有一些解决这些情况的捷径吗?

Also, doing some conversion here with foo.name to cleanse it every time with every little thing, while on the one hand provides me compile-time guarantees and safety it is a big bother most of the time. Is there some short-hand to get around these scenarios?

推荐答案

您需要像这样的双感叹号:

You need double exclamation mark like so:

val bar = makeNewBar(foo.name!!)

无效安全"部分中所述:

As documented in Null Safety section:

第三个选项适用于NPE爱好者.我们可以写b !! 返回b的非空值(例如，在我们的示例中为String)或抛出 如果b为null，则为NPE:

The third option is for NPE-lovers. We can write b!!, and this will return a non-null value of b (e.g., a String in our example) or throw an NPE if b is null:

val l = b!!.length 

因此，如果您想要NPE，可以拥有它，但是必须明确要求它，并且它不会出现在NPE之外. 蓝色.

Thus, if you want an NPE, you can have it, but you have to ask for it explicitly, and it does not appear out of the blue.

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