Re: [boost] Re: in/out parameters, codingstylesandmaintenance

From: Noel Yap (Noel.Yap_at_[hidden])
Date: 2003-05-04 21:36:54

"Justin M. Lewis" wrote:
> I have thought about that, yes.  And, as these were first made, I'll go
> through their history again.  Originally it was only for out values, that
> was my original use.  I had discussions with some people on IRC, someone
> there split the code into 2 classes, out and in_out, and on top of that, he
> made them different.  out params did NOT allow you access to the internal
> object at all, it ONLY gave you a = operator so you could assign the
> internal object something.  Both classes at one point had asserts to make
> sure the internal data was modified in some way before the destruction of
> the out or in_out object.  I found that to be annoying, because I may not
> simply want to assign a value to an out object.  I may want to use one of
> its member functions to modify it, or initialize it.  So, I gave both
> classes cast operators, so I could get the internal data, then removed the
> assert, because it was in the way now.  Now, you MIGHT be able to set these
> classes up in such a way that you can access the member functions of an out
> object, but, not get a reference to it still, so you can't just grab it and
> start screwing with it however you want.  The problem is, you still have no
> way of determining which member functions inside the object depend on the
> current state of the object, and which ones don't.  So, ultimately, no
> matter how you do this, some of the burden of not breaking the system falls
> on the programmer.

OK.  What happens if we turn this around?

We're pretty sure we can't have pure out parameters (at least not
without a lot of pain).  Then again, we're almost certain we can have
pure in parameters.  So, why not use in_out<> for both out (since pure
out parameters don't exist in C++ anyway) and in/out parameters, and
in<> for pure in parameters?

> That's a good thing though, all that maintenance keeps us employed.

<sarcasm tone="friendly">
Ahh, yes, the worthy goal of staying employed rather than adding value
:-)
</sarcasm>

Noel