库对Scala的NotNull特性的支持 [英] Library support for Scala's NotNull trait

问题描述

注意::从Scala 2.11开始，不推荐使用NotNull.

Notice: As of Scala 2.11, NotNull is deprecated.

据我了解，如果您希望引用类型不可为空，则必须混入神奇的NotNull特性，编译器会自动阻止您在其中添加null -able值.例如，请参见此邮件列表线程.

As far as I understand, if you want a reference type to be non-nullable you have to mixin the magic NotNull trait, and the compiler will automatically prevent you from putting null-able values in it. See this mailing-list thread for instance.

缺少的是，对非空类型的不错的库支持.如果我想编写一个不需要直接连接Java代码的程序包，并且我想默认情况下阻止该程序包中的所有类型使用null，我别无选择，只能重新定义所有构建变量，例如

What lacking is, a decent library support for non-nullable types. If I would like to write a package that don't need to interface java code directly, and I want to prevent all types in this package from using null by default, I have no choice but to redefine all builting variables like so

//can't actually do that, but just to give the general idea
class NString extends String with NotNull
class NMap[X,Y] extends Map[X,Y] with NotNull
...

我希望scala具有(作为编译器插件或库)供我编写的选项

I expect scala to have (as a compiler plugin, or library) option for me to write

import collections.notnull._

以便轻松禁止在特定的scala文件中使用null.

in order to easily disallow null usage in a specific scala file.

是否可以轻松地将标准库中的许多有用类型强制为不可空?

Is there an option to easily force many usefull types in the standard library to be not-nullable?

推荐答案

我真的不知道与NotNull达成的交易是什么，但是我得到的印象是Scala尚未完全解决它想如何交易的问题.与NotNull/Nullable概念.我自己的政策是永远不要在Scala中使用null，并且如果您调用可能返回null的Java API，请立即将其转换为Option.

I don't really know what the deal is with NotNull, but I get the impression that Scala hasn't fully worked out how it wants to deal with NotNull/Nullable concepts. My own policy is to never use null in Scala, and if you call a Java API that may return null, immediately convert it to an Option.

此实用程序方法是我最好的朋友:

This utility method is my best friend:

def ?[A <: AnyRef](nullable: A): Option[A] = if (nullable eq null) None else Some(nullable)

然后您执行以下操作:

val foo: Option[Foo] = ?(getFooFromJavaAPIThatMightReturnNull())

我发现这比尝试跟踪可能为null或不为null的情况简单得多.

I find this far simplier than trying to track what may or may not be null.

所以我根本没有回答您的问题，但是我会继续讲下去，以防它有用...

So I didn't answer your question at all, but I pass this on in case it's useful...

更新:现在，最新的Scala版本在标准API中支持此功能:

Update: more recent Scala versions now support this in the standard API:

val foo: Option[Foo] = Option(getFooFromJavaAPIThatMightReturnNull())

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