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From: Jeffrey Faust (jefffaust_at_[hidden])
Date: 2007-05-23 00:24:59

Fernando Cacciola wrote:

> Hi Jeffrey,
> In my experience, changing the class layout based on a preprocessor
> switch is a very bad idea since it breaks binary compatibility with
> libraries compiled with a different switch, so I strongly suggest
> you/we find a better solution.

I agree. This is probably the largest drawback. I'll look further.

> If this functionality is really really needed (read below), I would
> create a *different* template class to offer it. One such
> debugger-friendly
> optional<> would replace (rather than add) the bool field with a T* field
> (which would be set to NULL when uninitialized). A different template
> class makes sure that binary-differing optional's don't mix accidentally
> (in the same wa a policy-based design does it).

I'll see what I can do with this. Perhaps this other class will wrap the
real boost::optional, providing the same interface, and giving an
additional debug value. This would make it easier to keep the two classes
in sync.

> But I'm curious: doesn't a simple dynamic watch, like "*opt", works??
> That calls a method on the object, yes, but debuggers have been able to
> do that for decades now.

Quite honestly, I couldn't answer this before I tried it. Using the
"Immediate Window" in VC8 gives the error "CXX0034: Error: types
incompatible with operator." Now this is a legitimate debugger problem.

Thanks for the idea,

Jeff Faust

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