Out parameters with RhinoMocks

Question

I'm obviously confused - this is a task I've accomplished with several other frameworks we're considering (NMock, Moq, FakeItEasy). I have a function call I'd like to stub. The function call has an out parameter (an object).

The function call is in a use case that is called multiple times within the code. The calling code hands in parameters, including a NULL object for the out parameter. I'd like to set up an expected OUT parameter, based on the other parameters provided.

How can I specify an expected INBOUND out parameter of NULL, and an expected OUTBOUND out parameter of an object populated the way I expect it? I've tried it six ways to Sunday, and so far haven't been able to get anything back but NULL for my OUTBOUND out parameter.

Answer 1

From http://ayende.com/wiki/Rhino+Mocks+3.5.ashx#OutandRefarguments:

Ref and out arguments are special, because you also have to make the compiler happy. The keywords ref and out are mandantory, and you need a field as argument. Arg won't let you down:

User user;
if (stubUserRepository.TryGetValue("Ayende", out user))
{
  //...
}
stubUserRepository.Stub(x =>
  x.TryGetValue(
    Arg.Is("Ayende"), 
    out Arg<User>.Out(new User()).Dummy))
  .Return(true);

out is mandantory for the compiler. Arg.Out(new User()) is the important part for us, it specifies that the out argument should return new User(). Dummy is just a field of the specified type User, to make the compiler happy.

Answer 2

In case using repository to generate Mock/Stub

checkUser = MockRepository.GenerateMock<ICheckUser>

You can setup expectation with out parameter

checkUser
.Expect(c => c.TryGetValue(Arg.Is("Ayende"), out Arg<User>.Out(new User()).Dummy)
.Return(true)