Re: [boost] Report from Mont Tremblant C++ Committee meeting

From: Fernando Cacciola (fernando_cacciola_at_[hidden])
Date: 2005-10-17 15:14:30

Joel de Guzman wrote:
> David Abrahams wrote:
>> Joel de Guzman <joel_at_[hidden]> writes:
>>
>>> I think this is again an artifact of the confusion between the
>>> dual interfaces that optional provides. optional has an identity
>>> crisis of being a pointer (as the author's original model) and
>>> a variant<T, nil> (which I suggested later on). The rebinding
>>> behavior that Fernando rationalized was long and winding and
>>> confusing. I don't recall anymore his exact rationale. All I
>>> know is that when you have to explain your design using so much
>>> wordings, then something is wrong, and I don't buy the gobbledegook.
>>
>>
>> I *really* don't have an opinion about what the right choice should
>> be.  That said, terms like gobbledegook seem needlessly judgemental,
>> and as such I think they only cloud the issues.
>
> But, IMO, it *is* unclear and wordy jargon (http://tinyurl.com/954xg)
> I find the explanation very difficult to follow.

I wonder what explanation you are referring to?
You still haven't addressed the very issue that forms the core of that 
explanation.

> I don't agree that
> I am being judgemental. IMO, it's important for a model to be
> as simple as possible. If a certain aspect of a library cannot be
> explained in clear and concise manner, then that will potentially
> lead to misinterpretations, loopholes and gotchas later on.
>
And I totally agree..
But if a design causes misinterpretations, loopholes and gotchas later on, 
then it might look like being as simple as possible while in reality is 
over-simplified.
Without rebinding semantics, that is, over-simplifying the problem, 
assignment can do 2 totally different things. That's a source for 
misinterpretations, loopholes and gotchas.

> [SNIP]

> Of course you need an assignment operator... and structs do
> provide a guide: The point is that you can't rebind it.

Yes you can.. you meant you shouldn't.

> You can do anything with it, and in the common case, just assign the
> rhs to the lhs,

What if thre is no rhs to assign to??

> but you cannot rebind it. That is why I often
> switch between the "tuple" model, the "variant" model and the
> "struct" model. Both follow the struct model. And, by the struct
> model, what I am referring to is the limits on what you can do.
> Sure you need to have an assignment to a struct to give it sensible
> semantics. But you can't rebind. That IMO, is the sensible behavior
> when you are embedding/holding a reference.
>
That is a sensible behaviour when embeeding a reference that never 
references nothing.
If your model supports nullability, that is, the reference can reference 
nothing, then _consistent_ rebinding is a reasonable choice.

Best

-- 
Fernando Cacciola
SciSoft
http://fcacciola.50webs.com/