从方法返回泛型类型的实例

Question

我想有一个方法getInstance,它接受一个字符串值并返回一个对象的实例,在方法签名中定义为泛型

  def getInstance[T](dataStr: String): Option[T] = {
      T match {
        case typeOf[String] => Some(dataStr)             // if type of T is String 
        case typeOf[Integer] => Some(dataStr.toInt)      // if type of T is Integer
        case typeOf[Boolean] => Some(dataStr.toBoolean)  // if type of T is Boolean
        case _ => throw new NoSuchElementException()
      }
  }

如何在Scala中编写相同的内容？

Scala版本:2.11

Answer 1

类型类可能是最好的解决方案.

trait FromString[T] {
  def apply(s: String): T
}

object FromString {
  implicit object IntString extends FromString[Int] {
    def apply(s: String) = s.toInt
  }
  implicit object DoubleString extends FromString[Double] {
    def apply(s: String) = s.toDouble
  }
  implicit object BooleanString extends FromString[Boolean] {
    def apply(s: String) = s.toBoolean
  }
}

def getInstance[T](dataStr: String)(implicit from: FromString[T]): Option[T] =
  Some(from(dataStr))

val a = getInstance[Int]("1")
val b = getInstance[Double]("1.0")
val c = getInstance[Boolean]("true")

这将为有效类型提供编译时检查,getInstance并将返回相应的Option类型.