如何识别没有底层java字段的scala构造函数参数'fields'？

Question

我在scala中玩反射.我选择了

class CloneSubject(val a :Int, b :String, private var c :Boolean)

作为主题并迭代typeOf[CloneSubject].members以查找fields(sym.isTerm && (sym.asTerm.isVar || sym.asTerm.isVal))但是当我尝试创建FieldMirror时,(cm mirrorField sym.asTerm)我得到此异常:

Exception in thread "main" scala.ScalaReflectionException: Scala field b isn't represented as a Java field, 
neither it has a Java accessor method
note that private parameters of class constructors don't get mapped onto fields and/or accessors,
unless they are used outside of their declaring constructors.` 

现在,我完全理解为什么会发生这种情况,但我无法找到一种方法来检查这一点而不会抛出异常.当然,使用Java反射工作得很好,但那是违背这一点的.有任何想法吗？

Answer 1

为了避免错误，请b提前过滤掉：

scala> val m = reflect.runtime.universe.runtimeMirror(getClass.getClassLoader)
m: reflect.runtime.universe.Mirror = JavaMirror with ...

scala> val im = m.reflect(new CloneSubject(5, "hello", true))
im: reflect.runtime.universe.InstanceMirror = instance mirror for CloneSubject@2a95e173

scala> val fields = typeOf[CloneSubject].members collect { case m: MethodSymbol if m.isGetter => m.accessed }
fields: Iterable[reflect.runtime.universe.Symbol] = List(variable c, value a)

scala> fields map (s => im.reflectField(s.asTerm).get)
res45: Iterable[Any] = List(true, 5)

你知道每个可访问的字段都有一个Getter，因此唯一要做的就是获取所有现有Getter 所代表的字段。

另一个使用它来检查 val/var 是否有 Getter 的选项：

scala> typeOf[CloneSubject].members.filter(s => s.isTerm && (s.asTerm.isVar || s.asTerm.isVal) && s.asTerm.getter != NoSymbol)
res50: Iterable[reflect.runtime.universe.Symbol] = SynchronizedOps(variable c, value a)