Re: [boost] Formal review: Optional library

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] * http://www.boost-consulting.com
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