Re: [boost] Formal review: Optional library

From: Joel de Guzman (djowel_at_[hidden])
Date: 2002-12-10 17:49:42

----- Original Message ----- 
From: "Fernando Cacciola" <fernando_cacciola_at_[hidden]>

> > > optional captures the zero/one distinction, which, as its analogy to
> > > pointers makes clear, is a very useful one.  A type which can contain
> > > any number of different types would have a much more complicated
> > > interface.  Maybe it's just a different library?
> >
> > Or perhaps, optional is just a limited add-on API over the variant?
> > The low-level  implementation mechanism in place seems to be very
> > similar and having 2 separate libraries will be redundant, I think.
> >
> Not so...
> The low-level implementation is like a variant ONLY is the wrapped object is
> not a POD.
> When you have, say, optional<int>, the implementation uses: struct { int
> m_value ; bool m_initialized }
> As a result, value access, via operator*() is more efficient since it
> doesn't dereference a pointer.

That depends on how the variant is implemented. Which variant
implementation are you referring to? I'm sorry. I'm confused with
what you are saying. I can't see why it is more efficient. Neither do
I see a dereference in any case.

Joel de Guzman
joel_at_[hidden]
http://www.boost-consulting.com