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

Subject: Re: [Boost-users] [ptr_container] ptr_map and cloning issues
From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2009-02-06 07:30:14

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.

-Thorsten