Please help me learn STL

Quote:

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Everyone knows that you can use STL containers on polymorphic data but since you cannot inherit (safely) from STL types, people assume that you cannot have run-time polymorphic STL objects (ie. Run-time determination of what container type you are passing into an algorithm).
This can easily be achieved through a custom iterator type that contains a polymorphic member. In this way, the exterior iterator type (your custom iterator) passed to the algorithm is static, yet the iterator forwards operations to a polymorphic member whose type is run-time dependent.

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That was a short quote from someone. But I have a hard time understanding his words and how to write a piece of code as to exemplify what he says.
for example

Code:

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template<typename T>
class MyList:public std::list<T>
{
};

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Why is this supposed to be unsafe ?
Thank you

Quote:

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Originally Posted by terminalXXX

That was a short quote from someone. But I have a hard time understanding his words and how to write a piece of code as to exemplify what he says.
for example

Code:

---

template<typename T>
class MyList:public std::list<T>
{
};

---

Why is this supposed to be unsafe ?
Thank you

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Code:

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int main()
{
  std::list<int> *pList = new MyList<int>;
  delete pList;
}

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The behaviour is undefined, since std::list<int> has no virtual destructor.

Regards,

Paul McKenzie