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

From: Felipe Magno de Almeida (felipe.almeida_at_[hidden])
Date: 2005-03-10 17:09:21

What I was needing was a map of sets, then it wasnt compiling because of 
the operator[]. I modified the ptr_set for my imediate need, but I think 
Ill do as you said, use a pointer container. Now it really seems to me 
more obvious why not allow copy construction.
The same as you cant push_front in a vector, I think it shouldnt be 
possible to copy construct a pointer container.

Thorsten Ottosen wrote:
> "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 
> 
> 
> 
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-- 
    Felipe Magno de Almeida
    UIN: 2113442
     email: felipe.almeida at ic unicamp br, felipe.m.almeida at gmail 
com, felipe at synergy com
I am a C, modern C++, MFC, ODBC, Windows Services, MAPI developer
from synergy, and Computer Science student from State
University of Campinas(UNICAMP).
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