[boost] Re: Re: Re: Re: stl-like containers of pointers

From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2005-03-10 16:08:10

"Felipe Magno de Almeida" <felipe.almeida_at_[hidden]> wrote in message 
news:4230A997.7090101_at_ic.unicamp.br...

| > yes, but this is no ordinary std::vector. std::vector is for 
self-contained
| > value types; boost::ptr_vector is for pointers whose life-time
| >  must be managed.
| >
| > | boost::vector<A> vector1, vector2;
| > | vector1 = vector2;
| >
| > boost::ptr_vector don't have an assignment operator; it is not Assignable 
nor
| > CopyConstructible.
| >
| > you must clone or release the container:
| >
| > vector1 = vector2.clone();
| > vector1 = vector2.release();
| >
|
| I see, but it makes impossible for use ptr_containers inside other
| containers. Isnt this too restrictive?

well, yes, you would have to use a pointer container.

ptr_vector< ptr_list<Foo> > vec;
vec.push_back( new ptr_list<Foo>  );

when move semantics enters the langauge, they can become movable.

| Cant they be implemented in terms of these?

yes.

| There were a discussion about this before? So that I can know the
| reasons why?

I can't remember any long discussion, but I know why I made the choice.

The types stored in a pointer container need not be copyable; most
uses will be non-copyable objects or clonable objects. Neither
type of object can be copied and hence it seems wrong to
allow a container of them to be copied; it kinda hides the true nature
of the contained objects.

Moreover, copying a whole container can be really expensive; it seems better
that the distinction between copyable and clonable objects carries over to
the containers as well so users are reminded of the distinction.

br

-Thorsten