Re: [boost] New Library Proposal: dual_state

From: David Abrahams (dave_at_[hidden])
Date: 2005-07-15 13:01:16

Andrey Melnikov <melnikov_at_[hidden]> writes:

> Rob Stewart wrote:
>> From: "Jost, Andrew" <Andrew_Jost_at_[hidden]>
>> 
>>>But you're assuming that we have control over the library.  That's
>>>probably the exception rather than the rule in real life.
>> 
>> If you can change the library to use an adaptor for an optional,
>> why can't you change the library to use the optional directly?
>> 
>
> Adapters work outside the library and don't require any changes to the 
> library. Library requires underlying values, and with the adapter it 
> gets them automagically. The library doesn't know anything about 
> Optional and adapters, library clients do.

FYI, I might tend to use a dual_state object that either yields a
contained _reference_ or the result of invoking a function, because
you usually don't want to pay for copy construction of a contained
object if you don't have to, and it feels nonuniform to have 
lightweight copy only when the default is going to be used.

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