用构造函数和伴随对象扩展类

Question

I would like extend the following class and companion

object MyData { // code inside }
class MyData(val data: Struct) extends AnyVal { // code inside }

but get Illegal inheritance from value error when doing try to do this

class MyDataExtended(override val data: Struct) extends MyData(data)

Answer 1

Taken From: http://docs.scala-lang.org/overviews/core/value-classes.html

Prior to Scala 2.10, AnyVal was a sealed trait. Beginning with Scala 2.10, however, it is possible to define a subclass of AnyVal called a ''user-defined value class'' which is treated specially by the compiler. Properly-defined user value classes provide a way to improve performance on user-defined types by avoiding object allocation at runtime, and by replacing virtual method invocations with static method invocations.

Limitations

Value classes currently have several limitations, in part because the JVM does not natively support the concept of value classes. Full details on the implementation of value classes and their limitations may be found in SIP-15.

Summary of Limitations

1. must have only a primary constructor with exactly one public, val parameter whose type is not a value class. (From Scala 2.11.0, the parameter may be non-public.)

2. may not have specialized type parameters.

3. may not have nested or local classes, traits, or objects

4. may not define a equals or hashCode method.

5. must be a top-level class or a member of a statically accessible object.

6. can only have defs as members. In particular, it cannot have lazy vals, vars, or vals as members.

7. cannot be extended by another class.