克隆分配器,以及 boost::p tr_container 中的多态性

Clone allocators, and polymorphism in boost::ptr_container

本文关键字:container 多态性 tr 分配器 以及 boost      更新时间:2023-10-16

对于我当前的项目,我正在使用boost::ptr_vector来多态地保存Objects,并且一切正常,直到我的一个构建VS2010抛出它无法克隆object所以我去了,并查找克隆,并按照boost的要求实现了new_clone()方法,并按照c ++常见问题解答使其pure virtual, 但是现在VS2010向我抛出这个shanagin,说它不能在抽象类上使用克隆。

1>c:program filesboostboost_1_49_0boostptr_containerclone_allocator.hpp(34): error C2259: 'Object' : cannot instantiate abstract class
1>          due to following members:
1>          'Object *Object::new_clone(void) const' : is abstract
1>          c:...Object.h(36) : see declaration of 'Object::new_clone'
1>          c:program filesboostboost_1_49_0boostptr_containerclone_allocator.hpp(68) : see reference to function template instantiation 'T *boost::new_clone<U>(const T &)' being compiled
1>          with
1>          [
1>              T=Object,
1>              U=Object
1>          ]
1>          c:program filesboostboost_1_49_0boostptr_containerdetailreversible_ptr_container.hpp(110) : see reference to function template instantiation 'U *boost::heap_clone_allocator::allocate_clone<Object>(const U &)' being compiled
1>          with
1>          [
1>              U=Object
1>          ]
1>          c:program filesboostboost_1_49_0boostptr_containerdetailreversible_ptr_container.hpp(99) : while compiling class template member function 'Object *boost::ptr_container_detail::reversible_ptr_container<Config,CloneAllocator>::null_clone_allocator<allow_null_values>::allocate_clone(const Object *)'
1>          with
1>          [
1>              Config=boost::ptr_container_detail::sequence_config<Object,std::vector<void *,std::allocator<void *>>>,
1>              CloneAllocator=boost::heap_clone_allocator,
1>              allow_null_values=false
1>          ]
1>          c:program filesboostboost_1_49_0boostptr_containerdetailreversible_ptr_container.hpp(276) : see reference to class template instantiation 'boost::ptr_container_detail::reversible_ptr_container<Config,CloneAllocator>::null_clone_allocator<allow_null_values>' being compiled
1>          with
1>          [
1>              Config=boost::ptr_container_detail::sequence_config<Object,std::vector<void *,std::allocator<void *>>>,
1>              CloneAllocator=boost::heap_clone_allocator,
1>              allow_null_values=false
1>          ]
1>          c:program filesboostboost_1_49_0boostptr_containerdetailreversible_ptr_container.hpp(275) : while compiling class template member function 'void boost::ptr_container_detail::reversible_ptr_container<Config,CloneAllocator>::null_policy_deallocate_clone(const Object *)'
1>          with
1>          [
1>              Config=boost::ptr_container_detail::sequence_config<Object,std::vector<void *,std::allocator<void *>>>,
1>              CloneAllocator=boost::heap_clone_allocator
1>          ]
1>          c:program filesboostboost_1_49_0boostptr_containerptr_sequence_adapter.hpp(132) : see reference to class template instantiation 'boost::ptr_container_detail::reversible_ptr_container<Config,CloneAllocator>' being compiled
1>          with
1>          [
1>              Config=boost::ptr_container_detail::sequence_config<Object,std::vector<void *,std::allocator<void *>>>,
1>              CloneAllocator=boost::heap_clone_allocator
1>          ]
1>          c:program filesboostboost_1_49_0boostptr_containerptr_vector.hpp(35) : see reference to class template instantiation 'boost::ptr_sequence_adapter<T,VoidPtrSeq,CloneAllocator>' being compiled
1>          with
1>          [
1>              T=Object,
1>              VoidPtrSeq=std::vector<void *,std::allocator<void *>>,
1>              CloneAllocator=boost::heap_clone_allocator
1>          ]
1>          c:generaldevseniortankbattle3dtankbattle3dtankbattle3droom.h(28) : see reference to class template instantiation 'boost::ptr_vector<T>' being compiled
1>          with
1>          [
1>              T=Object
1>          ]

这是否意味着为了能够克隆东西,我必须扔掉抽象基类?


笔记:

  • 在任何时候,程序中都不应该存在抽象基类的对象,但几乎所有内容都将被视为这样。
  • 当我使克隆方法非虚拟,并为其提供实际返回某些内容的方法(提供一个构造函数/复制构造函数,这意味着它们可以存在,这违背了设计(,然后编译器抛出所有派生类都需要一个默认构造函数。 没有它们是设计使然。

编辑:我没有实现delete_clone()(不知道这是明确要求的,我认为析构函数会做得很好(

class Object{
public :
    ObjectType  superType;
    bool toBeRemoved;
    virtual void performAction(int action, Object& source){}
    virtual void updateObject(float duration){}
    virtual ~Object(){}
    virtual Object * new_clone(void)const = 0;      // Object.h[36]
    bool operator==(const Object& _other)const;
    bool operator!=(const Object& _other)const;
};

你想要的是一个独立的(非成员(new_clone()函数,编译器将优先于Boost clone_allocator.hpp中的函数

class Object{
public :
    ObjectType  superType;
    bool toBeRemoved;
    virtual void performAction(int action, Object& source){}
    virtual void updateObject(float duration){}
    virtual ~Object(){}
    bool operator==(const Object& _other)const;
    bool operator!=(const Object& _other)const;
private:
    virtual Object * do_clone() const = 0;
};
// in the same namespace as `class Object`:
//  so it will get picked up instead of Boost's default 
//  implementation
inline
Object* new_clone( const Object& o)
{
    return o.do_clone();
}