我有以下代码,用Scala 2.10.0编写:
trait A[T <: B] {
self : { def foo() } =>
val action : ()=>Unit = this.foo _
//wanna make default for this
val construction : String=>T
def bar()(implicit x : String) : T = {
action()
val destination = construction(x)
destination.baz()
destination
}
}
trait B { def baz() {} }
class Xlass { def foo() {} }
class Klass(a : String)(implicit val x : String) extends B {
val f = new Xlass with A[Klass] {
//boilerplate!
val construction = new Klass(_)
}
}
implicit val x = "Something"
val destination = new Klass("some a").f.bar()
我想知道,是否可以为construction
设置默认值,例如val construction = new T(_)
?目前我已经尝试了几个选项,但没有一个能满足此代码的所有特性,例如使用类型边界、隐式和结构类型。就我所能得到的而言,这是一个,但它在scala.ScalaReflectionException: free type T is not a class
:中失败了
import reflect.runtime.universe._
val tT = weakTypeTag[T]
...
val privConstruction =
x : String =>
runtimeMirror(tT.mirror.getClass.getClassLoader)
//fails here with scala.ScalaReflectionException: free type T is not a class
.reflectClass(tT.tpe.typeSymbol.asClass)
.reflectConstructor(tT.tpe.members.head.asMethod)(x).asInstanceOf[T]
所以,最后,我做到了:
trait A[T <: B] {
self : { def foo() } =>
val action : ()=>Unit = this.foo _
def construction(x: String)(implicit tag : reflect.ClassTag[T]) : T = {
tag.runtimeClass.getConstructor(classOf[String], classOf[String]).newInstance(x, x).asInstanceOf[T]
}
def bar()(implicit x : String, tag : reflect.ClassTag[T]) : T = {
action()
val destination = construction(x)
destination.baz()
destination
}
}
trait B { def baz() {} }
class Xlass { def foo() {} }
class Klass(a : String)(implicit val x : String) extends B {
val f = new Xlass with A[Klass]
}
implicit val x = "Something"
val destination = new Klass("some a").f.bar()