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POATL COM - How To Reuse Code for Interface Method
 

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  1. POATL COM - How To Reuse Code for Interface Method
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    <p>I have several interfaces, e.g. IA, IB, IC, and so on, that share common properties, e.g. Site. I would like to know how to reuse code for these interfaces (please save me the answer on COM aggregation).</p> <p>Current implementation is as follows:</p> <pre><code>class CA // ATL specific... { STDMETHODIMP get_Site(...) {...} STDMETHODIMP put_Site(...) {...} } class BA // ATL specific... { STDMETHODIMP get_Site(...) {...} STDMETHODIMP put_Site(...) {...} } class CC // ATL specific... { STDMETHODIMP get_Site(...) {...} STDMETHODIMP put_Site(...) {...} } </code></pre> <p>What I want to achieve (but cannot) is as follows. </p> <pre><code>template&lt;typename T&gt; class SharedProperties { STDMETHODIMP get_Site(...) {...} STDMETHODIMP put_Site(...) {...} } class CA : // ATL specific... SharedProperties&lt;CA&gt; { // properties are inherited and are accessible from IC } class BA // ATL specific... SharedProperties&lt;CB&gt; { // properties are inherited and are accessible from IB } class CC // ATL specific... SharedProperties&lt;CC&gt; { // properties are inherited and are accessible from IA } </code></pre> <p>I came across this idea after reading up (<a href="http://vcfaq.mvps.org/com/7.htm" rel="nofollow">http://vcfaq.mvps.org/com/7.htm</a>) but the site does not have a working example and no matter how much I tried I could not get it to work. I keep getting "Cannot instantiate abstract class" because the pure virtual functions get_Site and put_Site are not implemented (as per the second snippet).</p> <p><strong>EDIT</strong> Do note that I am using VS2010. Sample implementation below:</p> <pre><code>class ATL_NO_VTABLE CArticle : public CComObjectRootEx&lt;CComSingleThreadModel&gt;, public CComCoClass&lt;CArticle, &amp;CLSID_Article&gt;, public IDispatchImpl&lt;IArticle, &amp;IID_IArticle, &amp;LIBID_GeodeEdiLib, /*wMajor =*/ 1, /*wMinor =*/ 0&gt; { public: CArticle() { } </code></pre>
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    1. COWhich class is abstract and can't be instantiated?
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    2. COShouldn't `SharedProperties::get_Site` and `SharedProperties::put_Site` be virtual?
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      1. POATL COM - How To Reuse Code for Interface Method
      1. USJoe Gauterin
    3. COThey are, but if you are familiar with ATL I am sure you will get the point. The snippet is not actual source code. It is there for illustration purposes only.
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