Idiomatic replacement for existential types
scala
Solution
The warning is about the inference of existential type, which is usually undesirable. Either add the import statement, or make it explicit:
val key: (Class[_], String) = (klass, id)
Problem
I have some Scala code that uses existential types that I'm upgrading to 2.10, and I noticed a warning about adding "import language.existentials" which makes me think there should be a better way to write this. The code I have boils down to: ``` class A { private var values = Set.empty[(Class[_], String)] def add(klass: Class[_], id: String) { val key = (klass, id) if (!values(key)) { values += key // More logic below.. } } ``` I get this warning: ``` [warn] test.scala:4 inferred existential type (Class[_$2], String) forSome { type _$2 }, which cannot be expressed by wildcards, should be enabled [warn] by making the implicit value language.existentials visible. [warn] This can be achieved by adding the import clause 'import language.existentials' [warn] or by setting the compiler option -language:existentials. [warn] See the Scala docs for value scala.language.existentials for a discussion [warn] why the feature should be explicitly enabled. [warn] val key = (klass, id) ``` Is there a way I can rewrite my code not generate this warning (or require the import), or is that the most idiomatic way to express it? I never ask about the type parameter of Class anywhere in the code.