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.

score 22 · Answer 1 · answered Sep 26 '11 at 17:58

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.

The link now gets a 404 Not Found. – jakejgordon Feb 01 '16 at 17:50 — jakejgordon, Feb 01 '16 at 17:50

score 6 · Answer 2 · answered Sep 26 '12 at 10:02

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)

score 6 · Answer 3 · answered Jan 17 '14 at 21:24

6

This solution is cleaner and works fine with Rhino Mocks 3.6:

myStub.Stub(x => x.TryGet("Key", out myValue))
      .OutRef("value for the out param")
      .Return(true);

answered Jan 17 '14 at 21:24

Marcelo Oliveira

653
5
16

This is the only way that worked for me. It wouldn't recognize the `out Arg.Out` syntax. +1 – inejwstine Aug 17 '20 at 23:26
I would also add that as of C# 7.0, you can use an underscore as a discard for the `out` variable, simplifying it further to `x.TryGet("Key", out _)` (which also saves you from having to declare `myValue` elsewhere). – inejwstine Aug 17 '20 at 23:29

Out parameters with RhinoMocks

3 Answers3