dynamic_cast的继承和用法

Question

假设我有3个类如下(因为这是一个例子,它不会编译!):

class Base
{
public:
   Base(){}
   virtual ~Base(){}
   virtual void DoSomething() = 0;
   virtual void DoSomethingElse() = 0;
};

class Derived1
{
public:
   Derived1(){}
   virtual ~Derived1(){}
   virtual void DoSomething(){ ... }
   virtual void DoSomethingElse(){ ... }
   virtual void SpecialD1DoSomething{ ... }
};

class Derived2
{
public:
   Derived2(){}
   virtual ~Derived2(){}
   virtual void DoSomething(){ ... }
   virtual void DoSomethingElse(){ ... }
   virtual void SpecialD2DoSomething{ ... }
};

我想创建Derived1或Derived2的实例,具体取决于在运行时之前不可用的某些设置.

由于我无法在运行时确定派生类型,那么您认为以下是不好的做法吗？...

class X
{
public:
   ....

   void GetConfigurationValue()
   {
      ....
      // Get configuration setting, I need a "Derived1"
      b = new Derived1();

      // Now I want to call the special DoSomething for Derived1
      (dynamic_cast<Derived1*>(b))->SpecialD1DoSomething();      
   }
private:
   Base* b;
};

我一般都认为dynamic_cast的用法很糟糕,但正如我所说,我不知道在运行时要创建哪种类型.请帮忙!

Answer 1

如果类型信息通过将指向派生的指针分配给指向base的指针,为什么不延迟你"抛弃"某些时刻:

void GetConfigurationValue()
{
  // ...
  // Get configuration setting, I need a "Derived1"
  Derived1* d1 = new Derived1();
  b = d1;

  // Now I want to call the special DoSomething for Derived1
  d1->SpecialD1DoSomething();
}