相关疑难解决方法(0)

在某些用例中,创建对象的副本很有用,该对象是一组案例类的案例类的实例,它们具有共同的特定值.

例如,让我们考虑以下案例类:

case class Foo(id: Option[Int])
case class Bar(arg0: String, id: Option[Int])
case class Baz(arg0: Int, id: Option[Int], arg2: String)

然后copy可以在每个案例类实例上调用:

val newId = Some(1)

Foo(None).copy(id = newId)
Bar("bar", None).copy(id = newId)
Baz(42, None, "baz").copy(id = newId)

如此处和此处所述,没有简单的方法来像这样抽象:

type Copyable[T] = { def copy(id: Option[Int]): T }

// THIS DOES *NOT* WORK FOR CASE CLASSES
def withId[T <: Copyable[T]](obj: T, newId: Option[Int]): T =
  obj.copy(id = newId)

所以我创建了一个scala宏,它完成了这项工作(几乎):

import scala.reflect.macros.Context

object Entity {

  import …

我想编写一个Scala宏,它将一个case类的实例作为参数.可以传递给宏的所有对象都必须实现特定的标记特征.

以下代码段显示了标记特征和实现它的两个示例案例类:

trait Domain
case class Country( id: String, name: String ) extends Domain
case class Town( id: String, longitude: Double, latitude: Double ) extends Domain

现在,我想使用宏编写以下代码,以避免运行时反射的严重性及其线程不安全:

object Test extends App {

  // instantiate example domain object
  val myCountry = Country( "CH", "Switzerland" )

  // this is a macro call
  logDomain( myCountry )
} 

宏logDomain在不同的项目中实现,看起来类似于:

object Macros {
  def logDomain( domain: Domain ): Unit = macro logDomainMacroImpl

  def logDomainMacroImpl( c: Context )( domain: c.Expr[Domain] ): c.Expr[Unit] = { …

我正在编写REST Web服务的包装器,我想要强类型的Scala API.

以下是我到目前为止所做的事情:

def getMentions(count: Option[Int] = None,
                sinceID: Option[TweetID] = None,
                maxID: Option[TweetID] = None,
                trimUser: Option[Boolean] = None,
                contributorDetails: Option[Boolean] = None,
                includeEntities: Option[Boolean] = None) : List[Tweet] = {
val parameters = Map("count" -> count,
                     "since_id" -> sinceID,
                     "max_id" -> maxID,
                     "trim_user" -> trimUser,
                     "contributor_details" -> contributorDetails,
                     "include_entities" -> includeEntities)
/* 
 * Convert parameters, which is a Map[String,Any] to a Map[String,String]
 * (Removing Nones) and pass it to an object in charge of generating the request. …