Open
Description
Compiler version
3.3.3
Minimized code
object Example:
//Scala 2 library method (scala.Function0)
val f: Function0[Int] = () => 42
f.apply // <==== Why no error here?
f.apply()
//Scala 3 library method
scala.Tuple.apply
scala.Tuple.apply()
scala.runtime.Scala3RunTime.assertFailed
scala.runtime.Scala3RunTime.assertFailed()
// User code
class A {
def apply(): Int = 42
}
val a = new A()
a.apply
a.apply()Expectation
Compiler should generate error "method apply in class Function0 must be called with () argument" for f.apply similar to all other method calls without ()
See https://docs.scala-lang.org/scala3/reference/changed-features/eta-expansion-spec.html
If m is has an empty argument list (i.e. has type ()R):
If the expected type is of the form () => T, we eta expand.
If m is defined by Java, or overrides a Java defined method, we insert ().
Otherwise we issue an error of the form: method must be called with () argument
