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POCovariant virtual functions return type problem
 

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    <p>I have following code:</p> <pre><code>#include &lt;iostream&gt; using namespace std; class Child1 { int i; }; class Child2 : public Child1 { int j; }; class Base1 { public: virtual Child1&amp; getChildren() { cout &lt;&lt; "Children1" &lt;&lt; endl; return children; } private: Child1 children; }; class Base2 : public Base1 { public: virtual Child2&amp; getChildren() { cout &lt;&lt; "Children2" &lt;&lt; endl; return children; } private: Child2 children; }; </code></pre> <p>This code compiles fine but when I change the return type of <code>getChildren()</code> from reference type to object type in either or both <code>Base1</code> and <code>Base2</code> (e.g. <code>virtual Child2 getChildren()</code>, I get the following error on Visual Studio 2010:</p> <pre><code>error C2555: 'Base2::getChildren': overriding virtual function return type differs and is not covariant from 'Base1::getChildren' </code></pre> <p>I want to know why am I <strong>not</strong> getting this error when using reference and getting it otherwise. Is this is a bug in VS2010? Because the C++ standard (according to <a href="http://support.microsoft.com/kb/240862" rel="nofollow">this</a> page on Microsoft's website) says something like: <em>The return type of an overriding function shall be either identical to the return type of the overridden function or covariant with the classes of the functions.</em> And <em>the class in the return type of B::f is the same class as the class in the return type of D::f or, is an unambiguous direct or indirect base class of the class in the return type of D::f and is accessible in D.</em></p> <p>P.S. I do not have access to the standard at the moment so can not verify the above quote.</p>
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    1. COAre you sure it happens, if you change BOTH to object type?
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      1. USDaniel Hilgarth
    2. CO@Daniel Hilgarth: Yes. Compiling the above code with these two methods `virtual Child1 getChildren()` and `virtual Child2 getChildren()` also gives the same error.
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