def merge[X](list1: Option[List[X]], list2: Option[List[X]]): Option[List[X]]  
def merge[X](list1: Option[List[X]], elem: Option[X]): Option[List[X]]

The compiler says that these two functions have same type after erasure

def merge[X](list1: Option[List[X]],list2: Option[List[X]]): Option[List[X]] at line 122 and
def merge[X](list1: Option[List[X]],elem: Option[X]): Option[List[X]] at line 131
have same type after erasure: (list1: Option, list2: Option)Option

Why does the Option[List[X]] and Option[X] become same after erasure? How can I make them different?

CodePudding user response：

• Why does the Option[List[X]] and Option[X] become same after erasure?

Cause the generic type parameter of Option[...] is erased (so both X and List[X] are erased) so both methods will have the same signature.

• How can I make them different?

One approach - adding dummy implicit parameter to one of the methods so they have different signatures:

def merge[X](list1: Option[List[X]], list2: Option[List[X]]): String = "1"
def merge[X](list1: Option[List[X]], elem: Option[X])(implicit d: DummyImplicit): String = "2"

println(merge(Some(List(1)), Some(List(2)))) // 1

println(merge(Some(List(1)), Some(2))) // 2