You should definitely get a compiler error...
scala> :paste
// Entering paste mode (ctrl-D to finish)
trait MyTrait extends BaseClass {
def myAbstractMethod: MyReturnType
def myConcreteMethod = { /*implementation*/ }
}
class MyClass extends BaseClass with MyTrait {
}
// Exiting paste mode, now interpreting.
<console>:14: error: class MyClass needs to be abstract, since method myAbstractMethod in trait MyTrait of type => MyReturnType is not defined
class MyClass extends BaseClass with MyTrait {
^