Re: [boost] New Library Proposal: dual_state

From: David Abrahams (dave_at_[hidden])
Date: 2005-07-11 14:05:41

"Fernando Cacciola" <fernando_cacciola_at_[hidden]> writes:

> "David Abrahams" <dave_at_[hidden]> escribió en el mensaje 
> news:uoe9abw3k.fsf_at_boost-consulting.com...
>> "Jost, Andrew" <Andrew_Jost_at_[hidden]> writes:
>>
>>>>From: boost-bounces_at_[hidden]
>>> [mailto:boost-bounces_at_[hidden]] On Behalf Of Eelis van der Weegen
>>>
>>>>Jost, Andrew wrote:
>>>>> I am curious if there is support for what I'm calling a "dual_state"
>>>>> template class.
>>>> From your description it sounds a lot like Boost.Optional. What are
>>> the main differences?
>>>>Eelis
>>>
>>> I'll admit I did not even pause at Boost.optional when I scanned the
>>> library listing for previous work, a failure in my ability to connect
>>> the description, "Discriminated-union wrapper for optional values," with
>>> the concept I had in mind.
>>
>> Oh, you're right!  That is a terrible one-line description, because
>>
>>  a. It uses technical terms that many people probably don't know
>>     "discriminated union"
>>
>>  b. optional doesn't really act like a union (in any way that matches
>>     my intuition)!  I understand the theoretical connection, of
>>     course, but nobody is thinking that way when they read brief
>>     descriptions.
>>
> Very good point.
> Right now I can think of
>
> "A library to wrap and manipulate values can be be 'optional': that is, 
> (explicitely) uninitialized"
>
> but that doesn't sound very inspired.
>
> Any proposals?

A container that uses no dynamic memory and holds at most one element:
optional<T> can hold any value of T or none at all.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com