使用enable_shared_from_this

使用enable_shared_from_this

说明
The header <boost/enable_shared_from_this.hpp> defines the class template enable_shared_from_this. It is used as a base class that allows a shared_ptr to the current object to be obtained from within a member function.
继承该类就可以进行基于当前子类进行安全的weap_ptr到shared_ptr的转换...

代码实例
以下代码中Y类继承enable_shared_from_this,, 从而我们可以直接在函数中调用shared_from_this获得该对象的shared_ptr

class Y:public enable_shared_from_this<Y>
{
public:

    shared_ptr<Y> f()
    {
        return shared_from_this();
    }
}

int main()
{
    shared_ptr<Y> p(new Y);
// 调用f获得shared_ptr

    shared_ptr<Y> q = p->f();
    assert(p == q);
    assert(!(p < q|| q< p));// p and q must share ownership

}

该类的实现

template<class T>class enable_shared_from_this
{
protected:

    enable_shared_from_this()
    {
    }

    enable_shared_from_this(enable_shared_from_this const&)
    {
    }

    enable_shared_from_this & operator=(enable_shared_from_thisconst&)
    {
        return *this;
    }

    ~enable_shared_from_this()
    {
    }

public:

    shared_ptr<T> shared_from_this()
    {
        shared_ptr<T> p(_internal_weak_this);
        BOOST_ASSERT(p.get() == this);
        return p;
    }

    shared_ptr<T const> shared_from_this()const
    {
        shared_ptr<T const> p(_internal_weak_this);
        BOOST_ASSERT(p.get() == this);
        return p;
    }

// Note: No, you don't need to initialize _internal_weak_this

//

// Please read the documentation, not the code

//

// http://www.boost.org/libs/smart_ptr/enable_shared_from_this.html


    typedef T _internal_element_type; // for bcc 5.5.1

    mutable weak_ptr<_internal_element_type> _internal_weak_this;
};



结论
这个实用类提供了简单的shared_ptr转换和安全的weak式验证... 这样通过继承就可以使用shared_from_this进行安全当前类weak_ptr到shared_ptr的转换...