Re: [boost] ptr_container: ptr_map_adapter interface

From: axter (boost_at_[hidden])
Date: 2006-01-04 01:04:50

"Thorsten Ottosen" <tottosen_at_[hidden]> wrote in message
news:<dpf7ec$9kl$1_at_[hidden]>...
> axter wrote:
> > 
>  >
> > I think the cow_ptr should be used as the default method for 
> > creating containers of pointers, and that the current boost pointer 
> > containers should be used when memory management is the more 
> > important factor for a particular requirement.
> 
> Their primary purpose is to facilitate OOP in C++. This domain is
> sufficiently different from the value-based domain that different 
> programming idioms apply.
> 
> 
> > I'm not sure about the ptr_set and ptr_map classes, because I 
> > haven't seen any example code usage that would have it work with an 
> > abstract type.
> 
> Listen, when you said you could get it to work with an abstract type, 
> I
> tried it out.
> 
> It works fine, but one gets errors if one does not define new_clone() 
> for the abstract type:
> 
> namespace Foo
> {
>    struct abtract_base { ... };
> 
>    inline new_clone( const abstract_base& r )
>    { return r.clone(); }
> }
> 
> My guess is that most of the other compile problems go away when you
> define this.
> 
> Did you not read
> 
> http://www.boost.org/libs/ptr_container/doc/reference.html#the-clonabl
> e-concept

I did read it, and if you read my code, you would see that the new_clone
function is in the shape.h header.

I just tested it again, and again it fails to compile.
I even went through the trouble of taking out all the compiler directives,
and cleaning the code so-as to remove any possible noise, but it still fails
to compile.

One of the compile errors is becaue boost::ptr_map class requires the object
have a default constructor.
After I added a default constructor for test purposes, it still fail to
compile, by giving the following error:
****************************************************************************
*********************************************************
c:\lib\boost_1_33_0\boost\ptr_container\ptr_map_adapter.hpp(171) : error
C2259: 'Shape' : cannot instantiate abstract class
        due to following members:
        'void Shape::draw(void) const' : pure virtual function was not
defined
        m:\__Current\PolymorphicContainersDemo\shape_test.h(12) : see
declaration of 'Shape::draw'
        'std::string Shape::GetShapeName(void) const' : pure virtual
function was not defined
        m:\__Current\PolymorphicContainersDemo\shape_test.h(13) : see
declaration of 'Shape::GetShapeName'
        'Shape *Shape::do_clone(void) const' : pure virtual function was not
defined
        m:\__Current\PolymorphicContainersDemo\shape_test.h(33) : see
declaration of 'Shape::do_clone'
        c:\lib\boost_1_33_0\boost\ptr_container\ptr_map_adapter.hpp(161) :
while compiling class-template member function
'boost::ptr_container_detail::ptr_map_adapter_base<T,VoidPtrMap,CloneAllocat
or>::reference
boost::ptr_container_detail::ptr_map_adapter_base<T,VoidPtrMap,CloneAllocato
r>::insert_lookup(const
boost::ptr_container_detail::ptr_map_adapter_base<T,VoidPtrMap,CloneAllocato
r>::key_type &)'
****************************************************************************
*********************************************************

I get the above error from the following four lines of code:
                boost::ptr_map<int, Shape> mIntToShape;
                int i123 = 123;
                mIntToShape.insert(i123, new Circle("blue"));
                mIntToShape[i123].draw(); //This line is what causes the
error

You can download the shape class from following link:
http://code.axter.com/shape_test.h

Have you tested this code with an abstract type, and if so, can you post the
test code?