Scala反射：为什么getMethods返回超类中定义的私有val？

Question

Code below defines a trait T with a private val someVal and an anonymous class extending T . If we call getMethods from the instance of the anonymous class, someVal is listed as a public method:

scala> trait T { private val someVal = 3 }
defined trait T

scala> new T {}.getClass.getMethods.apply(0)
res2: java.lang.reflect.Method = public int $anon$1.$line6$$read$T$$someVal()

Of course someVal isn't accessible in this subclass, but why is it even in the return of getMethods , as public?

Answer 1

trait s compile to interfaces , because they need multiple-inheritance. But interfaces can have neither fields nor non- public members. Therefore, a field becomes a pair of public accessors, mangled by the trait's name, and the compiler is tasked with placing the field into all subclasses and implementing the accessors. Any methods on T trying to access someVal go through the getter, and the static $init$ function, which contains the constructor code, uses the setter to set it to 3 . If your val were declared public , then the name of the getter would be demangled to just someVal , and external code would use that, and if it were also var , the setter would demangle to someVal_= , which subsequently mangles to someVal_$eq . The horribly long mangled names are pretty much enough to keep anyone from using them, anyway, and it's only relevant when doing Java interop.