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POWhat's the simplest way to satisfy a pure abstract method with methods from other base classes
 

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  1. POWhat's the simplest way to satisfy a pure abstract method with methods from other base classes
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    <p><strong>Edit:</strong> Per some comments, by simple I mean a) less code, b) easy to maintain, and c) hard to get wrong.</p> <p><strong>Edit #2:</strong> Also, using containment instead of private inheritance is not objectionable if it does indeed simplify the implementation of <code>InterfaceImpl</code>.</p> <p>Currently, the only way I know to do this is to have the implementer define the abstract method and delegate the call to the target base type's method. Example:</p> <pre><code>#include &lt;iostream&gt; #include &lt;memory&gt; class Interface { public: virtual void method1() = 0; virtual void method2(int x) = 0; }; class MethodOneImpl { private: void method1(int x) { std::cout &lt;&lt; "MethodOneImpl::method1() " &lt;&lt; x &lt;&lt; std::endl; } public: void method1() { method1(0); } }; class MethodTwoImpl { public: void myFunc(int x) { std::cout &lt;&lt; "MethodTwoImpl::myFunc(x)" &lt;&lt; x &lt;&lt; std::endl; } }; class InterfaceImpl : public Interface , private MethodOneImpl , private MethodTwoImpl { public: virtual void method1() { MethodOneImpl::method1(); } virtual void method2(int x) { MethodTwoImpl::myFunc(x); } }; int main() { std::unique_ptr&lt;Interface&gt; inf; inf.reset(new InterfaceImpl); inf-&gt;method1(); inf-&gt;method2(0); // This should be disallowed! // std::unique_ptr&lt;MethodOneImpl&gt; moi; // moi.reset(new InterfaceImpl); } </code></pre> <p>At first, I thought that perhaps this might solve the problem:</p> <pre><code>class InterfaceImpl : public Interface , private MethodOneImpl , private MethodTwoImpl { public: using MethodOneImpl::method1; // Obviously this wouldn't work as the method names don't match. //using MethodTwoImpl::??? }; </code></pre> <p>The first using statement will make both <code>MethodOneImpl::method1</code> methods be public, but it actually doesn't fulfill the contract with <code>Interface</code>, and it modifies the accessibility of <code>MethodOneImpl::method1(int)</code>. And obviously we couldn't use this solution with <code>method2</code> as the names don't match up.</p> <p>FWIW, I have what I think is a solution, but it is not part of the standard at all (in other words it won't compile). I was thinking of making a proposal to the C++ committee; if anyone has any advice, I'd appreciate any comments below (but please dont' submit the advice as an answer).</p>
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    1. COWhat is the problem with the delegating code? Why don't you want to use that?
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    2. CO@Mat Because there might be more than two abstract methods, and I'd rather not have half the bytes in my source be hard-to-maintain boilerplate.
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    3. COHard to maintain? That's write-once one-liners. You'd have to maintain whatever mapping syntax you can come up with too.
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