类型参数不符合特质减去的的类型参数界限

Question

升级到斯卡拉2.12，我有这个代码的一个奇怪的编译问题后：

val c = Map("a" -> Set[Map[String, String]](), "b" -> Map[String, String]()) 

它抛出这个异常：

Error:(19, 7) type arguments [?,Iterable[Equals] with String with scala.collection.immutable.Map[String,String] => Any with scala.collection.generic.Subtractable[_ >: String with scala.collection.immutable.Map[String,String] <: Object, Iterable[Equals] with String with scala.collection.immutable.Map[String,String] => Any with scala.collection.generic.Subtractable[_ >: String with scala.collection.immutable.Map[String,String] <: Object, Iterable[Equals] with String with scala.collection.immutable.Map[String,String] => Any with scala.collection.generic.Subtractable[_ >: String with scala.collection.immutable.Map[String,String] <: Object, Equals]]{def seq: Iterable[Equals] with String with scala.collection.immutable.Map[String,String] => Any with scala.collection.generic.Subtractable[_ >: String with scala.collection.immutable.Map[String,String] <: Object, Equals]}]{def seq: Iterable[Equals] with String with scala.collection.immutable.Map[String,String] => Any with scala.collection.generic.Subtractable[_ >: String with scala.collection.immutable.Map[String,String] <: Object, Iterable[Equals] with String with scala.collection.immutable.Map[String,String] => Any with scala.collection.generic.Subtractable[_ >: String with scala.collection.immutable.Map[String,String] <: Object, Equals]]{def seq: Iterable[Equals] with String with scala.collection.immutable.Map[String,String] => Any with scala.collection.generic.Subtractable[_ >: String with scala.collection.immutable.Map[String,String] <: Object, Equals]}}] do not conform to trait Subtractable's type parameter bounds [A,+Repr <: scala.collection.generic.Subtractable[A,Repr]] 

Answer 1

它看起来像一个错误。如果模拟不存在，您可以将其发布到bug tracker。

解决方法尝试将值附加到映射。

scala> val c = Map.empty[String,Iterable[Any]] + ("a" -> Set[Map[String, String]]()) + ("b" -> Map[S 
tring, String]()) 
c: scala.collection.immutable.Map[String,Iterable[Any]] = Map(a -> Set(), b -> Map())