CODEWITHSUNDEEP
scalafunctional-programming
tribbloid
tribbloid

Reputation: 3838

Scala throws no type parameters error on valid lambda definition

The following method definition:

  def validClasses(dataType: DataType) = {
    examples
      .flatMap {
        v: Any =>
          Try {
            val canon = toCanonicalType(v, dataType)
            canon.getClass
          }
            .toOption
            .toSet
      }
  }

yield the following error:

Error:(94, 8) no type parameters for method flatMap: (f: Any => scala.collection.GenTraversableOnce[B])(implicit bf: scala.collection.generic.CanBuildFrom[scala.collection.immutable.Set[Any],B,That])That exist so that it can be applied to arguments (Any => scala.collection.immutable.Set[Class[?0]] forSome { type ?0 })
 --- because ---
argument expression's type is not compatible with formal parameter type;
 found   : Any => scala.collection.immutable.Set[Class[?0]] forSome { type ?0 }
 required: Any => scala.collection.GenTraversableOnce[?B]
      .flatMap {
   ^

Which is strange. As the result of toSet is not a a Set[Class[?0]] forSome { type ?0 }. Is there any way to fix this problem?

Upvotes: 0

Views: 213

Answers (1)

Alexey Romanov
Alexey Romanov

Reputation: 170713

As the result of toSet is not a a Set[Class[?0]] forSome { type ?0 }.

Yes, it is: .getClass returns a Class[_], so Try { ... } is a Try[Class[?0]] forSome { type ?0 } (?0 is just a variable name generated by the compiler), and .toOption.toSet is a Set[Class[?0]] forSome { type ?0 }.

Upvotes: 1

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