为什么shared_ptr没有虚拟析构函数？(Why doesn't shared_ptr have a virtual descructor? (and how can I get around this?))

 我想制作一个特殊版本的shared_ptr ，它可以在创建或销毁时执行特定的操作，但我的计划似乎因为认识到shared_ptr的析构函数是非虚拟的而被挫败，这意味着当我覆盖它时，我的指针永远不会得到当它们的最后一个实例被销毁时清理干净。 
 
 想到的唯一选择是将此行为构建到我想要与我的假设自定义shared_ptr一起使用的每个类中，这是不可行的（或者在某些情况下可能）。 
 
 编辑： 
 
 我想要这个的原因是因为我想在lua中使用一些类作为userdata对象，并且我希望我使用这种方式的每个对象都有一个独特的fenv表，当所有引用都被清理时对象已被删除。 我打算使用指针的地址，因为它们键入一个包含fenv表的表。 
 
 让我们说我有一个小部件可以有其他小部件作为孩子。 我在Lua中创建了两个小部件，然后将一个小部件设置为另一个小部件，并删除对子小部件的所有lua引用（事实上它是一个用C ++处理的子节点）。 GC现在可以随时运行并移除孩子。 我不一定希望孩子运行它的析构函数，所以我想让它成为一个shared_ptr。 这样，在Lua清理它之后，C ++对象仍然可以使用它。 如果我已将值或函数分配给它的fenv，我仍然希望能够访问它们。 只有在删除对子窗口小部件的最终引用时，才能完全删除fenv tabled。 

I wanted to make a special version of shared_ptr that would perform specific operations when it was created or destroyed, but my plans appear to be foiled by the realization that shared_ptr's destructor is non virtual, meaning when I override it, my pointers never get cleaned up when the last instance of them are destroyed.
 
The only alternative that comes to mind is to build in this behavior into every class that I want to use with my hypothetical custom shared_ptr, and that's not feasible (or possible in some cases). 
 
Edit:
 
The reason I want this is because I want to use some classes as userdata objects in lua, and I want each one of my objects that I use this way to have a fenv table unique to it that will be cleaned up when all references to the object have been removed. I plan on using the address of the pointer as they key into a table that holds the fenv table.
 
Lets say I have a widget that can have other widgets as children. I create two widgets in Lua, then set one as the child of the other and remove all lua references to the child widget (the fact that it's a child is handled in C++). The GC can now run at any time and remove the child. I don't necessarily want the child to have it's destructor run though, so I want to make it a shared_ptr. That way, C++ objects can still use it after Lua has cleaned it up. If I've assigned values or functions to it's fenv I still want to be able to access them. Only when the final reference to my child widget is removed do I want the fenv tabled to be removed totally.

原文：https://stackoverflow.com/questions/3801648