polymorphic(带多态性质的)base classes应该声明一个virtual析构函数。如果class带有任何virtual函数，它就应该拥有一个virtual析构函数。
Classes的设计目的如果不是作为base classes使用，或不是为了具备多态性(polymorphically)，就不应该声明virtual析构函数。
Effective C++:条款07:为多态基类声明virtual析构函数 (Declare destructors virtual in polymorphic base classes.)
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You got a dream
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People can't do something themselves
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You got a dream
You gotta protect it
People can't do something themselves
They wanna tell you you can do it
If you want something
Go get it