使用隐式默认值

Question

我想了解使用Mockito和Scala默认参数的一些行为。

这是一个最小的例子：

trait SomeImplicit

object SomeService {
  val AnyImplicit = new SomeImplicit {}
}

trait SomeService {
  def doWork(param: String)(implicit di: SomeImplicit = SomeService.AnyImplicit)
}

让我们调用doWork方法：

class SomeService$Test extends WordSpec with MockitoSugar {
  "SomeService" should {
    "doWork" in {
      val dodo = mock[SomeService]
      val expectedParameter = "ok"

      dodo.doWork(expectedParameter)

      verify(dodo, times(1)).doWork(expectedParameter)(SomeService.AnyImplicit)
      verifyNoMoreInteractions(dodo)
    }
  }
}

自然而然地，虽然它会起作用但是我会这样做。但事实并非如此。我明白了：

Argument(s) are different! Wanted:
someService.doWork(
    "ok",
    SomeService$$anon$1@264c1c97
);
-> at SomeService$Test$$anonfun$1$$anonfun$apply$mcV$sp$1.apply$mcV$sp(SomeService$Test.scala:25)
Actual invocation has different arguments:
someService.doWork(
    "ok",
    null
);
-> at SomeService$Test$$anonfun$1$$anonfun$apply$mcV$sp$1.apply$mcV$sp(SomeService$Test.scala:23)

Argument(s) are different! Wanted:
someService.doWork(
    "ok",
    SomeService$$anon$1@264c1c97
);
-> at SomeService$Test$$anonfun$1$$anonfun$apply$mcV$sp$1.apply$mcV$sp(SomeService$Test.scala:25)
Actual invocation has different arguments:
someService.doWork(
    "ok",
    null
);
-> at SomeService$Test$$anonfun$1$$anonfun$apply$mcV$sp$1.apply$mcV$sp(SomeService$Test.scala:23)

Answer 1

带有默认值的隐式参数告诉编译器：如果通常的隐式搜索过程找不到隐式参数，请使用此值而不是发出编译错误。

始终在第一步中找到

DummyImplicit（使用Predef.dummyImplicit），因此永远不会使用默认值。