Re: [boost] Interest in a clone_ptr class?

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2006-07-04 11:29:17

Matt Calabrese wrote:
> On 7/3/06, Thorsten Ottosen <thorsten.ottosen_at_[hidden]> wrote:

>>If value semantics are desired, then why not provide them directly?
>>Having polymorphic types with value semantics is fairly rare.
> 
> 
> 
> I'd say fairly rare simply because the tools to make it simple and efficient
> were never there.

Or because it is rarely needed.

> non-dynamically allocated objects with value semantics. I know I keep
> repeating myself, but I'm not sure exactly what it is that you don't
> understand.

I think I understand perfectly what you're trying to do, but I fail to 
see the need for it. I have never had the need to treat these two types 
of objects the same way. Never.

> It is a lot more work to write an efficient/correct standard container
> 
>>library, than to write the pointer container library on top of the
>>standard library. So I don't agree with "simpler" here.
> 
> 
> 
> Simpler for users, not necessarily for the programmer of the library. 

I don't agree with the statement that it is easier for users either.

> Anyone
> who knows the STL knows how to use a given type in an STL container. Using a
> clone_ptr in an STL container can be done with the same code one would write
> with any other type, though with an optimized internal implementation
> entirely transparent to the user. All a programmer needs to learn is the
> interface of a clone_ptr and they get container optimizations without any
> extra work. Then, if they really need to optimize further, they can look at
> additional operations provided by the specializations.

You overlook that quite a few polymorphic types are not even clonable, 
hence you can't provide copy-semantics for them, but only make them 
moveable.

>>Without a clone pointer type of concept, it is much more difficult to make
>>
>>
>>>the code both generic and efficient.
>>
>>Depends on your definition of efficient.
> 
> 
> 
> Alright, then
> by what definition of efficient are you refering to? 

I think the idea of specializing the entire container library is very 
bad, to say the least. For example, std::vector< std::vector< 
clone_ptr<T> > > will still behave like a super slow beast without 
move-semantics.

> when such semantics are required. Keep in mind that this is not intended as
> a replacement for ptr_containers, I just offer it as a suggested replacement
> for a subset of usage of them which can potentially make working with
> generic code much easier for both library writers and users.

I fail to see the usage to be common enough to justify a rewrite of the 
all the containers. That is a *major* low-level task.

>>If you think you doing programmers a favor by muddling the distinction
>>between value semantics and polymorphic semantics, I think you're wrong.
> 
> 
> 
> I appreciate your criticisms, but I still disagree entirely. 

Ok, fair enough.

-Thorsten