I am trying to extend a class from a Java library and override the base method, but Eclipse keeps giving me errors even though the method signature is correct.
My code looks like this:
import someLibrary.ClassA
import someLibrary.TypeX
import someLibrary.TypeY
...
class MyClass extends ClassA {
...
override def foo(s: TypeX, params: Array[String]): List[TypeY] = {
...
}
}
The error I keep getting is:
overriding method foo in class ClassA of type (x$1: someLibrary.TypeX,
x$2: Array[String])java.util.List[someLibrary.TypeY]; method foo has
incompatible type
Note that my method signature is exactly the same.
EDIT:
After reading Ren's answer here's how I fixed it:
import scala.collection.JavaConverters._
myScalaList.asJava
It could be that the original method is returning a java.util.List, while your override is returning a Scala list.
Related
For a mocked class I have a method for which I would like to test whether there are no more interactions then needed, which looks similar to:
def someMethod(someMandatoryParam: Int, canBeDefaultIds: Option[Ids] = None): Future[Failures] = {...}
when I am mocking to invoke this method without the default parameter and I verify it that way:
verify(someClass).someMethod(someInt)
and then check if there was no more interactions:
verifyNoMoreInteractions(someClass)
I am getting an error that here was some unexpected interactions.
But when in implementation I change this method to use None instead of default value and verify:
verify(someClass).someMethod(someInt, None)
verifyNoMoreInteractions(someClass)
It works correctly.
Is there a problem with Mocikto and default values in Scala?
Default arguments is Scala specific feature which Java Mockito is likely not aware of. Consider how Scala code looks after -Xprint:jvm phase
abstract trait SomeClass extends Object {
def someInt(a: Option): Option = a;
<synthetic> def someInt$default$1(): Option = scala.None;
}
Notice how the default argument became just another method someInt$default$1. Try using mockito-scala which is designed with Scala in mind, for example the following test passes
import org.mockito.{ArgumentMatchersSugar, IdiomaticMockito}
import org.scalatest.flatspec.AnyFlatSpec
import org.scalatest.matchers.should.Matchers
trait SomeClass {
def someInt(a: Option[Int] = None) = a
}
class MockitoScalaDefaultArgsSpec extends AnyFlatSpec with Matchers with IdiomaticMockito with ArgumentMatchersSugar {
"mockito-scala" should "handle default arguments" in {
val someClass = mock[SomeClass]
someClass.someInt()
someClass.someInt() was called
someClass wasNever calledAgain
}
}
I'm trying to mock a method that returns an instance of a value class (extends AnyVal)
I'm getting some weird error message, which I understand (because of value class erasure) but I'm surprised Mockito doesn't cope with that.
My class:
case class MyValueClass(value: String) extends AnyVal
The function I want to mock:
trait ToMock {
def something(someParams: String): MyValueClass
}
And the mock:
val theMock = mock[ToMock]
val returned = MyValueClass("test")
when(theMock.something("test")).thenReturn(returned)
This code generates the following error:
MyValueClass cannot be returned by something()
something() should return String
But of course, if I make it return a String, it doesn't compile anymore...
If I remove extends AnyVal, of course it works fine.
OK, I found an answer that works.
I need to use the older mockito style of doReturn
doReturn(returned.value).when(theMock).something("test")
Because it's not type-safe, it works.
Not fully satisfactory though, as I give up type safety.
I am trying to use Scala Meta to write an annotation so I can generate another case class from an existing object.
But when I try to do this:
MyObject.parse[Source].show[Structure]
I got this error:
Error:(5, 20) not enough arguments for method parse: (implicit convert: scala.meta.common.Convert[domain.MyObject.type,scala.meta.inputs.Input], implicit parse: scala.meta.parsers.Parse[scala.meta.Source], implicit dialect: scala.meta.Dialect)scala.meta.parsers.Parsed[scala.meta.Source].
Unspecified value parameters convert, parse, dialect.
MyObject.parse[Source].show[Structure];}
^
I am very confused because based on their tutorial, that's what I need to start with
http://scalameta.org/tutorial/#.parse[T]
How can I reflect this object to loop through all properties?
Thanks
parse[Source] parses text. You may try the following
import scala.meta._
"object MyObject".parse[Source].get.show[Syntax]
If you are creating annotation then it might look like:
#MyAnnotation
object MyObject
And in another module:
import scala.meta._
class MyAnnotation extends StaticAnnotation {
inline def apply(defn: Any): Any = meta {
defn.show[Syntax]
defn
}
}
I have the following code which uses spray-json to deserialise some JSON into a case class, via the parseJson method.
Depending on where the implicit JsonFormat[MyCaseClass] is defined (in-line or imported from companion object), and whether there is an explicit type provided when it is defined, the code may not compile.
I don't understand why importing the implicit from the companion object requires it to have an explicit type when it is defined, but if I put it inline, this is not the case?
Interestingly, IntelliJ correctly locates the implicit parameters (via cmd-shift-p) in all cases.
I'm using Scala 2.11.7.
Broken Code - Wildcard import from companion object, inferred type:
import SampleApp._
import spray.json._
class SampleApp {
import MyJsonProtocol._
val inputJson = """{"children":["a", "b", "c"]}"""
println(s"Deserialise: ${inputJson.parseJson.convertTo[MyCaseClass]}")
}
object SampleApp {
case class MyCaseClass(children: List[String])
object MyJsonProtocol extends DefaultJsonProtocol {
implicit val myCaseClassSchemaFormat = jsonFormat1(MyCaseClass)
}
}
Results in:
Cannot find JsonReader or JsonFormat type class for SampleAppObject.MyCaseClass
Note that the same thing happens with an explicit import of the myCaseClassSchemaFormat implicit.
Working Code #1 - Wildcard import from companion object, explicit type:
Adding an explicit type to the JsonFormat in the companion object causes the code to compile:
import SampleApp._
import spray.json._
class SampleApp {
import MyJsonProtocol._
val inputJson = """{"children":["a", "b", "c"]}"""
println(s"Deserialise: ${inputJson.parseJson.convertTo[MyCaseClass]}")
}
object SampleApp {
case class MyCaseClass(children: List[String])
object MyJsonProtocol extends DefaultJsonProtocol {
//Explicit type added here now
implicit val myCaseClassSchemaFormat: JsonFormat[MyCaseClass] = jsonFormat1(MyCaseClass)
}
}
Working Code #2 - Implicits inline, inferred type:
However, putting the implicit parameters in-line where they are used, without the explicit type, also works!
import SampleApp._
import spray.json._
class SampleApp {
import DefaultJsonProtocol._
//Now in-line custom JsonFormat rather than imported
implicit val myCaseClassSchemaFormat = jsonFormat1(MyCaseClass)
val inputJson = """{"children":["a", "b", "c"]}"""
println(s"Deserialise: ${inputJson.parseJson.convertTo[MyCaseClass]}")
}
object SampleApp {
case class MyCaseClass(children: List[String])
}
After searching for the error message Huw mentioned in his comment, I was able to find this StackOverflow question from 2010: Why does this explicit call of a Scala method allow it to be implicitly resolved?
This led me to this Scala issue created in 2008, and closed in 2011: https://issues.scala-lang.org/browse/SI-801 ('require explicit result type for implicit conversions?')
Martin stated:
I have implemented a slightly more permissive rule: An implicit conversion without explicit result type is visible only in the text following its own definition. That way, we avoid the cyclic reference errors. I close for now, to see how this works. If we still have issues we migth come back to this.
This holds - if I re-order the breaking code so that the companion object is declared first, then the code compiles. (It's still a little weird!)
(I suspect I don't see the 'implicit method is not applicable here' message because I have an implicit value rather than a conversion - though I'm assuming here that the root cause is the same as the above).
I have the following macro defining a class and returning an instance of that class (with Scala 2.10.2 and the macro plugin):
def test[T] = macro testImpl[T]
def testImpl[T : c.WeakTypeTag](c: Context): c.Expr[Any] = {
import c.universe._
val className = newTypeName("Test")
c.Expr { q"""
class $className {
def method = 1
}
new $className
"""}
}
When I call the macro:
case class Cat(name: String)
val t = test[Cat].method
I get the following error:
method method in class Test cannot be accessed in Test
val t = test[Cat].method
^
My overall goal is to use vampire methods and to use quasi-quotes to describe the generated class. How can I solve this error?
In my post on vampire methods I mention this workaround for this bug. For some reason you currently aren't able to see an anonymous class's methods on the instance returned from the macro unless you create a wrapper class that extends the class with the methods and return an instance of that, instead.
You're seeing the same bug from a slightly different angle. You've named the class with the methods you want to see on the returned instance's structural type, but you still need a wrapper. The following will work:
c.Expr { q"""
class $className {
def method = 1
}
new $className {}
"""}
Note that all I've done is add a pair of brackets to the line creating the instance, so that I get an instance of an anonymous class extending $className instead of just a $className.
I have no idea what's behind this bug, and I'm not sure if Eugene knows more. I did recently confirm that it's still around in the latest build of 2.11.