需要从案例 Class 的特征中引用伴随对象的特征
Need to Reference Trait on Companion Object From Trait on Case Class
我需要访问具有指定特征的伴侣 class -- 来自用于案例 classes 的特征。我几乎可以肯定 Scala 反射库可以做到这一点,但我还没有完全把它拼凑起来。
我在下面创建了需要一段 ???充满一些反射魔法。代码按原样编译和运行——由于缺少功能而发出通知。
我在 Whosebug 上看到的一些相关答案来自 2.10。请兼容 Scala 2.12。
import scala.reflect.{ClassTag, classTag}
//for companion object
//accesses Fields of the associated case class to ensure the correctness
//note: abstract class -- not a trait due to issues using ClassTag on a trait
abstract class SupportsField1Companion[T: ClassTag] {
//gets the names of all Fields on the associated case class
val fieldNamesOfInstancedClass: Array[String] =
classTag[T].runtimeClass.getDeclaredFields.map(_.getName)
//prints the name and fields of the associated case class -- plus extra on success
def printFieldNames(extra: String = ""): Unit = {
val name = classTag[T].runtimeClass.getCanonicalName
val fields = fieldNamesOfInstancedClass.reduceLeft(_ + ", " + _)
println(s"Fields of $name: $fields" + extra)
}
}
//for case classes
//IMPORTANT -- please do not parameterize this if possible
trait SupportsField1 {
//some data for printing
val field1: String = this.getClass.getCanonicalName + ": field1"
//should get a reference to the associated companion object as instance of SupportsFieldsCompanion
def getSupportsFieldsCompanion: SupportsField1Companion[this.type] = //this.type may be wrong
??? //TODO reflection magic required -- need functionality to retrieve companion object cast as type
//calls a function on the associated Companion class
def callPrintFuncOnCompanion(): Unit =
getSupportsFieldsCompanion.printFieldNames(s" -- from ${this.getClass.getCanonicalName}")
}
//two case classes with the SupportsFieldsCompanion trait to ensure data is accessed correctly
object ExampleA extends SupportsField1Companion[ExampleA] {}
case class ExampleA() extends SupportsField1 {
val fieldA: String = "ExampleA: fieldA"
}
object ExampleB extends SupportsField1Companion[ExampleB] {}
case class ExampleB() extends SupportsField1 {
val fieldB: String = "ExampleB: fieldB"
}
object Run extends App {
//create instanced classes and print some test data
val exampleA = ExampleA()
println(exampleA.field1) //prints "ExampleA: field1" due to trait SupportsFields
println(exampleA.fieldA) //prints "ExampleA: fieldA" due to being of class ExampleA
val exampleB = ExampleB()
println(exampleB.field1) //prints "ExampleB: field1" due to trait SupportsFields
println(exampleB.fieldB) //prints "ExampleB: fieldB" due to being of class ExampleB
//via the SupportsFieldsCompanion trait on the companion objects,
//call a function on each companion object to show that each companion is associated with the correct case class
ExampleA.printFieldNames() //prints "Fields of ExampleA: fieldA, field1"
ExampleB.printFieldNames() //prints "Fields of ExampleB: fieldB, field1"
//test access of printFieldNames on companion object from instanced class
try {
exampleA.callPrintFuncOnCompanion() //on success, prints "Fields of ExampleA: fieldA, field1 -- from ExampleA"
exampleB.callPrintFuncOnCompanion() //on success, prints "Fields of ExampleB: fieldB, field1 -- from ExampleB"
} catch {
case _: NotImplementedError => println("!!! Calling function on companion(s) failed.")
}
}
有很多方法可以做到这一点,但以下可能是最简单的方法之一,它不涉及对 Scala 的伴生对象 class 名称重整如何工作的假设:
def getSupportsFieldsCompanion: SupportsField1Companion[this.type] =
scala.reflect.runtime.ReflectionUtils.staticSingletonInstance(
this.getClass.getClassLoader,
this.getClass.getCanonicalName
).asInstanceOf[SupportsField1Companion[this.type]]
这可以按预期工作,但我可能会将其键入 SupportsField1Companion[_]
,理想情况下我可能会避免在 SupportsField1
上使用 public 引用 [=13] 的方法=]—实际上 理想情况下 我可能会完全避免这种方法,但如果您愿意,我认为上面的 ReflectionUtil
解决方案可能是合理的。
我需要访问具有指定特征的伴侣 class -- 来自用于案例 classes 的特征。我几乎可以肯定 Scala 反射库可以做到这一点,但我还没有完全把它拼凑起来。
我在下面创建了需要一段 ???充满一些反射魔法。代码按原样编译和运行——由于缺少功能而发出通知。
我在 Whosebug 上看到的一些相关答案来自 2.10。请兼容 Scala 2.12。
import scala.reflect.{ClassTag, classTag}
//for companion object
//accesses Fields of the associated case class to ensure the correctness
//note: abstract class -- not a trait due to issues using ClassTag on a trait
abstract class SupportsField1Companion[T: ClassTag] {
//gets the names of all Fields on the associated case class
val fieldNamesOfInstancedClass: Array[String] =
classTag[T].runtimeClass.getDeclaredFields.map(_.getName)
//prints the name and fields of the associated case class -- plus extra on success
def printFieldNames(extra: String = ""): Unit = {
val name = classTag[T].runtimeClass.getCanonicalName
val fields = fieldNamesOfInstancedClass.reduceLeft(_ + ", " + _)
println(s"Fields of $name: $fields" + extra)
}
}
//for case classes
//IMPORTANT -- please do not parameterize this if possible
trait SupportsField1 {
//some data for printing
val field1: String = this.getClass.getCanonicalName + ": field1"
//should get a reference to the associated companion object as instance of SupportsFieldsCompanion
def getSupportsFieldsCompanion: SupportsField1Companion[this.type] = //this.type may be wrong
??? //TODO reflection magic required -- need functionality to retrieve companion object cast as type
//calls a function on the associated Companion class
def callPrintFuncOnCompanion(): Unit =
getSupportsFieldsCompanion.printFieldNames(s" -- from ${this.getClass.getCanonicalName}")
}
//two case classes with the SupportsFieldsCompanion trait to ensure data is accessed correctly
object ExampleA extends SupportsField1Companion[ExampleA] {}
case class ExampleA() extends SupportsField1 {
val fieldA: String = "ExampleA: fieldA"
}
object ExampleB extends SupportsField1Companion[ExampleB] {}
case class ExampleB() extends SupportsField1 {
val fieldB: String = "ExampleB: fieldB"
}
object Run extends App {
//create instanced classes and print some test data
val exampleA = ExampleA()
println(exampleA.field1) //prints "ExampleA: field1" due to trait SupportsFields
println(exampleA.fieldA) //prints "ExampleA: fieldA" due to being of class ExampleA
val exampleB = ExampleB()
println(exampleB.field1) //prints "ExampleB: field1" due to trait SupportsFields
println(exampleB.fieldB) //prints "ExampleB: fieldB" due to being of class ExampleB
//via the SupportsFieldsCompanion trait on the companion objects,
//call a function on each companion object to show that each companion is associated with the correct case class
ExampleA.printFieldNames() //prints "Fields of ExampleA: fieldA, field1"
ExampleB.printFieldNames() //prints "Fields of ExampleB: fieldB, field1"
//test access of printFieldNames on companion object from instanced class
try {
exampleA.callPrintFuncOnCompanion() //on success, prints "Fields of ExampleA: fieldA, field1 -- from ExampleA"
exampleB.callPrintFuncOnCompanion() //on success, prints "Fields of ExampleB: fieldB, field1 -- from ExampleB"
} catch {
case _: NotImplementedError => println("!!! Calling function on companion(s) failed.")
}
}
有很多方法可以做到这一点,但以下可能是最简单的方法之一,它不涉及对 Scala 的伴生对象 class 名称重整如何工作的假设:
def getSupportsFieldsCompanion: SupportsField1Companion[this.type] =
scala.reflect.runtime.ReflectionUtils.staticSingletonInstance(
this.getClass.getClassLoader,
this.getClass.getCanonicalName
).asInstanceOf[SupportsField1Companion[this.type]]
这可以按预期工作,但我可能会将其键入 SupportsField1Companion[_]
,理想情况下我可能会避免在 SupportsField1
上使用 public 引用 [=13] 的方法=]—实际上 理想情况下 我可能会完全避免这种方法,但如果您愿意,我认为上面的 ReflectionUtil
解决方案可能是合理的。