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From: David Abrahams (dave_at_[hidden])
Date: 2002-12-10 16:30:24

"Joel de Guzman" <djowel_at_[hidden]> writes:

> ----- Original Message -----
> From: "Fernando Cacciola" <fernando_cacciola_at_[hidden]>
>> optional<> is trying to model using C++ a concept that
>> it is not really covered by the language, that of uninitialzed values.
>> It uses pointer semantics *just* because pointers are the only sort of
>> C++ objects which has a clear uninitialized state.
> Hi,
> Probably a dumb question but allow me to ask anyway:
> Wouldn't a more generic variant<T0, T1...TN> class do what the
> optional is trying to do? I feel that optional<T> is just a variant<T, nil_t>
> in disguise. Correct me if I'm wrong.

Someone once said that if a theorem in Physics involves numbers other
than zero, 1, or infinity, it's lacking in purity.

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?

                       David Abrahams
   dave_at_[hidden] *
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