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POCan I have polymorphic containers with value semantics in C++?
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  1. POCan I have polymorphic containers with value semantics in C++?
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    copied!<p>As a general rule, I prefer using value rather than pointer semantics in C++ (ie using <code>vector&lt;Class&gt;</code> instead of <code>vector&lt;Class*&gt;</code>). Usually the slight loss in performance is more than made up for by not having to remember to delete dynamically allocated objects.</p> <p>Unfortunately, value collections don't work when you want to store a variety of object types that all derive from a common base. See the example below.</p> <pre><code>#include &lt;iostream&gt; using namespace std; class Parent { public: Parent() : parent_mem(1) {} virtual void write() { cout &lt;&lt; "Parent: " &lt;&lt; parent_mem &lt;&lt; endl; } int parent_mem; }; class Child : public Parent { public: Child() : child_mem(2) { parent_mem = 2; } void write() { cout &lt;&lt; "Child: " &lt;&lt; parent_mem &lt;&lt; ", " &lt;&lt; child_mem &lt;&lt; endl; } int child_mem; }; int main(int, char**) { // I can have a polymorphic container with pointer semantics vector&lt;Parent*&gt; pointerVec; pointerVec.push_back(new Parent()); pointerVec.push_back(new Child()); pointerVec[0]-&gt;write(); pointerVec[1]-&gt;write(); // Output: // // Parent: 1 // Child: 2, 2 // But I can't do it with value semantics vector&lt;Parent&gt; valueVec; valueVec.push_back(Parent()); valueVec.push_back(Child()); // gets turned into a Parent object :( valueVec[0].write(); valueVec[1].write(); // Output: // // Parent: 1 // Parent: 2 } </code></pre> <p>My question is: Can I have have my cake (value semantics) and eat it too (polymorphic containers)? Or do I have to use pointers?</p>
 

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