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POC++: Is it possible to inherit the assignment operator?
 

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  1. POC++: Is it possible to inherit the assignment operator?
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    <p>The following C++ code doesn't compile:</p> <pre><code>class BaseA { protected: BaseA &amp;operator = (const BaseA &amp;rhs); }; template&lt;typename T&gt; class BaseB { public: T &amp;operator = (const T &amp;rhs) { return *static_cast&lt;T *&gt;(this); }; }; class Derived : public BaseA, public BaseB&lt;Derived&gt; { }; int main() { Derived foo; Derived bar; foo = bar; return 0; }; </code></pre> <p>When I try to compile this I get a complaint that <code>BaseA &amp;BaseA::operator = (const BaseA &amp;)</code> is undefined. There are several other questions like this on stackoverflow however they all seem to concern the compiler auto-generating a <code>Derived &amp;Derived::operator = (const Derived &amp;)</code> function which calls <code>BaseA::operator = (const BaseA&amp;)</code>. In this case though <code>Derived</code> should already be inheriting a function with that exact signature from <code>BaseB&lt;Derived&gt;</code>. If I follow the advice on another question and add <code>using BaseB&lt;Derived&gt;::operator =;</code> to <code>Derived</code> the compiler complains that <code>Derived &amp;operator = (const Derived &amp;)</code> cannot be overloaded.</p> <p>Is it simply not possible for a class to inherit this operator?</p> <p><strong>Edit:</strong> To be clear, I'm confused why the compiler is giving <code>Derived</code> a default <code>Derived &amp;operator = (const Derived &amp;)</code> when it already inherits <code>T &amp;operator (const T &amp;) where [T = Derived]</code> from <code>Base&lt;Derived&gt;</code>. I can understand why the default copy assignment operator would normally be created and override any inherited assignment operators but in this case <code>Derived</code> is inheriting an operator with <em>the exact same</em> signature as its copy assignment operator. Is there a way to write <code>BaseB</code> so that its subclasses use this operator?</p>
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    1. COI'm not sure how that error relates to your question. You're getting that error because you declared that function, but never defined it.
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      1. USDrew Dormann
    2. COThe compiler is quite right that you haven't defined `BaseA& operator=` since you've only declared it. Change it to `BaseA &operator = (const BaseA &rhs) = default;` and it will happily compile.
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      1. USYuushi
    3. COThe linker shouldn't care that it isn't defined because it should never be getting called. The only reason it would be getting called is if the compiler is generating its own Derived::operator = (const Derived &) function.
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