Re: [Boost-users] [ptr_container] ptr_map and cloning issues

Subject: Re: [Boost-users] [ptr_container] ptr_map and cloning issues
From: Robert Dailey (rcdailey_at_[hidden])
Date: 2009-02-06 09:56:35

On Fri, Feb 6, 2009 at 6:30 AM, Thorsten Ottosen <
thorsten.ottosen_at_[hidden]> wrote:

> Robert Dailey skrev:
>
>> I have a ptr_map as follows:
>>
>> typedef boost::ptr_map<std::string, Texture> TextureContainer;
>>
>> I only use forward declarations of Texture where needed. When I'm
>> iterating over an instance of TextureContainer, I expect to not have to do
>> more than use the forward declaration since technically we're only iterating
>> pointer values and the definition of Texture is not needed for this. So when
>> I do this:
>>
>> TextureContainer myTextures;
>> TextureContainer::const_iterator it = myTextures.find( "some key" );
>>
>> The above (second line) results in an extremely complex and long compiler
>> error, but the important part of the error says what I have pasted below.
>> Why is this error happening? Is it trying to clone Texture objects? This
>> shouldn't be happening.
>>
>> /boost/ptr_container/clone_allocator.hpp(34) : error C2514: 'rs::Texture'
>> : class has no constructors
>>        C:\IT\work\planb\components\rs/renderer/TextureFwd.hpp(6) : see
>> declaration of 'rs::Texture'
>>
>>  C:\IT\work\planb\third_party\boost\1_37_0\boost/ptr_container/clone_allocator.hpp(55)
>> : see reference to function template instantiation 'T
>> *boost::new_clone<U>(const T &)' being compiled/
>>
>
> Hm. I can't really recreate this with vc9. What compiler are you using?
>
> First, this compiles without any problems for me:
>
>    class Texture;
>    typedef boost::ptr_map<std::string,Texture> MapType;
>
>    void foo( const MapType& m )
>    {
>        //MapType map;
>        MapType::const_iterator i = m.find( "foo" );
>        //i = map.find( "foo" );
>    }
>
> Now, the uncommented does not compile because the destructor may need to
> delete objects of type Texture, and boost::check_delete() refuses to do that
> on incomplete types.

I'm using VC9 as well. If the find() and iterator assignment do not compile
for you then you are probably experiencing the same problem I am. Could you
explain why the type must be known at this point? If I were to use a
std::map<std::string, Texture*> I doubt I would have this problem. I was
expecting the same of ptr_map.

At first you said "...this compiles without any problems for me" and then
you said "...the uncommented does not compile...". So which is it?