在 Scala 中注释构造函数参数 [英] Annotating constructor parameters in Scala

问题描述

在编译为字节码时，注释构造函数参数似乎没有任何作用.我也没有收到编译器警告.

Annotating constructor parameters seems to do nothing when compiled to bytecode. I get no compiler warnings either.

以下有效.name 字段的 getAnnotations 返回 javax.annotation.Nullable.

The following works. getAnnotations for the name field returns javax.annotation.Nullable.

class Person {
    @Nullable var name: String = _;
}

以下不是，无论是 val 还是 var.

The following doesn't, neither with val or var.

class Person(@Nullable var name: String)

这可能不是故意的，所以是我遗漏了什么还是应该提交错误报告?

This is probably not intentional, so is there something I am missing or should I go file a bug report?

推荐答案

当您在构造函数参数上指定注释时，您需要指定应该注释的内容.

You need to specify what should get annotated when you specify annotations on constructor parameters.

为此，使用来自 scala.annotation.target 的一个或多个注释来注释您的注释，例如getter、setter 或在您的情况下 field:

To do that annotate your annotation with one ore more annotations from scala.annotation.target, e.g. getter, setter or as in your case field:

import annotation.target.field

class Person(@(Nullable @field) var name: String)

您也可以为此使用类型别名:

You can also use type aliases for that:

type NullableField = Nullable @field

class Person(@NullableField var name: String)

更新 Scala 2.12

现在这个特定的注解和其他注解在 scala.annotation.meta 包中，而不是 scala.annotation.target

Update Scala 2.12

Now this specific annotation and others are in the package scala.annotation.meta rather than scala.annotation.target

import scala.annotation.meta.{field, param}

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