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copy_traits_base Struct Template Reference

Compile-time branch on how to copy pointees. More...

#include <copy-traits.h>

Inheritance diagram for copy_traits_base:

[legend]List of all members.

Static Public Methods
T *	clone (T const &t)
void	destroy (T *t)

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Detailed Description

template<class T>
struct copy_traits_base< T >

Compile-time branch on how to copy pointees.

If we have a pointer to an abstract base of a polymorphic type, we cannot copy the content by simply calling operator new. Instead, we must use some virtual member function like clone(). This is a problem when using polymorphic types together with smart pointers (how do they copy the pointer?). Also, if we want to use the 'pimpl' idiom together with a smart pointer, we cannot call delete on the opaque pointer-to-impl inside the smart pointer.

These differences are hidden by T* copy_traits<T>::clone(const T&) and copy_traits<T>::destroy(T*) Default implementation in copy_traits_base for non-polymorphic types is simply operator new / delete.

For T being an abstract class, this implmentation has to be overridden with a method like T::clone() by specializing copy_traits<> for T.

For an opaque type, we can declare a specialization along with the forward declaration of the type:

    class impl;
    template<>
    struct copy_traits<impl> {
      static impl* clone  (impl const&);
      static void  destroy(impl*);
   };

and define the specialization with the definition of the type:

   class impl { ... };
   
   impl* copy_traits<impl>::clone  (impl const& i) { return new impl(i);}
   void  copy_traits<impl>::destroy(impl      * i) { delete i;}

Definition at line 56 of file copy-traits.h.

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Member Function Documentation

template<class T> T* copy_traits_base< T >::clone (  T const &    t )  [inline, static]

Reimplemented in copy_traits< testA >. Definition at line 57 of file copy-traits.h.

template<class T> void copy_traits_base< T >::destroy (  T *    t )  [inline, static]

Definition at line 58 of file copy-traits.h.

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The documentation for this struct was generated from the following file:

• Utility/copy-traits.h

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Copyright (c) Guntram Berti 1997-2002. See the GrAL Homepage for up-to-date information.

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