Resurrects duplicate handlers and explains all the bugs we can make

Question

I really don't like this in any way.

该提问来源于开源项目：openzipkin/brave

Answer 1

here's the problem that can sneak up on the next change to add a list parameter.

java

  static class ListBindingProblems {
     List<a> as;
     List<b> bs;

     A provideA() {
      return new AB();
    }
  }

   public void listBindingProblems() {
    context.register(ListBindingProblems.class);
    context.refresh();

    ListBindingProblems problems = context.getBean(ListBindingProblems.class);
    assertThat(problems.as).hasSize(1);
    // eventhough the user declared their bean method provideA as returning A, spring will look at
    // all types and magically fill here. What that means is you have to be defensive about dupes,
    // or make it impossible to create dupes by type hierarchy.
    assertThat(problems.bs).hasSize(1);
  }
</b></a>