Why are primitive types such as Int erased to Object in Scala?
autoboxing, scala, type-erasure
Solution
Couldn't it be the much more useful `java.lang.Integer`?
Yes, and that was even the case, once. Unfortunately, that leads to broken type signatures. That is, it is impossible to generate correct bytecode in all situations if `Int` is erased to `java.lang.Integer`.
There isn't a single ticket or commit about this, but the one that changed this particular behavior is scala/bug#4214, in this commit.
Problem
In Scala, ``` { x: Option[Int] => x } .getClass .getMethod("apply", classOf[Option[_]]) .getGenericParameterTypes ``` returns `Array(scala.Option<java.lang.Object>)`. I'd initially been expecting to see instead `Array(scala.Option<scala.Int>)`, but I see that `scala.Int` is a value class (extends `AnyVal`) 'whose instances are not represented as objects by the underlying host system'. I still don't understand the erasure to `Object`, though. Couldn't it be the much more useful `java.lang.Integer`?