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From: Noel Yap (Noel.Yap_at_[hidden])
Date: 2003-04-24 06:13:35

"Justin M. Lewis" wrote:
> in/out seems to be used fairly commonly in COM. I'm not sure I have any
> great examples off the top of my head, but I know they're commonly used.

I'm not a COM person, but I believe it's written in C. If so, then you
are correct that in/out parameters are more needed since noone would
want to create a struct for each multiple return type.

OTOH, C++ has templates to deal with this situation (ie boost::tuple<>)
so, qualifying my previous statement, in C++ I still see no need for
in/out parameters.

> And using pointers is part of what we're trying to avoid here. Like I said,
> I avoid using pointers whenever possible at this point.

I'm a little confused. Either you pass in the entire object or you pass
in a pointer (even if it's wrapped in another class). How is this new
class supposed to be implemented?

> And, again, the real intent here is to insure clarity at the point of
> invocation. In my case I'm looking at 100's of thousands of lines of code,
> written over the past 8 years. It's tiresome trying to chase down where
> values COULD have changed. In this setup you KNOW exactly what calls are
> changing parameter values, and it's enforced. As long as the library calls
> use the c_out and c_in_out classes people using the library are forced to
> conform to the format. So, 8 years, and a few million lines of code later,
> no one will wonder what might cause a variable they're tracking to change
> values.

I think if parameters are used for in parameters only and return values
are used for out parameters only, the same thing is achieved. For

  inOutValue = square( inOutValue );

vs (using an extension for generality):

  square( c_in_out< typeof( inOutValue ) >( inOutValue ) );


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