Scala返回未知类型的对象

Question

How can I save an object of unknown type in Scala and return it?

I have a couple of classes that are all instantiated from the same class like this

class And(lhs: ExprTree, rhs: ExprTree) extends ExprTree
class Or(lhs: ExprTree, rhs: ExprTree) extends ExprTree

and a function that needs to return an instance of said classes (ie And(lhs, rhs) but I have no prior knowledge which). I also need to store an instance of And() or Or() without prior knowledge which one it is.

Answer 1

val expr: ExprTree = ???

will give you an identifier which could take on the value of either an And or an Or .

Similarly,

def (...): ExprTree = ???

will give you a function which will return a value of either And or Or (assuming some appropriate parameters, represented here by ...).

This answer seems far too simple and obvious. But it also seems to satisfy what I think is your request.