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POIs it okay to inherit implementation from STL containers, rather than delegate?
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  1. POIs it okay to inherit implementation from STL containers, rather than delegate?
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    copied!<p>I have a class that adapts std::vector to model a container of domain-specific objects. I want to expose most of the std::vector API to the user, so that he/she may use familiar methods (size, clear, at, etc...) and standard algorithms on the container. This seems to be a reoccurring pattern for me in my designs:</p> <pre><code>class MyContainer : public std::vector&lt;MyObject&gt; { public: // Redeclare all container traits: value_type, iterator, etc... // Domain-specific constructors // (more useful to the user than std::vector ones...) // Add a few domain-specific helper methods... // Perhaps modify or hide a few methods (domain-related) }; </code></pre> <p>I'm aware of the practice of preferring composition to inheritance when reusing a class for implementation -- but there's gotta be a limit! If I were to delegate everything to std::vector, there would be (by my count) 32 forwarding functions!</p> <p>So my questions are... Is it really so bad to inherit implementation in such cases? What are the risks? Is there a safer way I can implement this without so much typing? Am I a heretic for using implementation inheritance? :)</p> <p><strong>Edit:</strong></p> <p>What about making it clear that the user should not use MyContainer via a std::vector&lt;> pointer:</p> <pre><code>// non_api_header_file.h namespace detail { typedef std::vector&lt;MyObject&gt; MyObjectBase; } // api_header_file.h class MyContainer : public detail::MyObjectBase { // ... }; </code></pre> <p>The boost libraries seem to do this stuff all the time.</p> <p><strong>Edit 2:</strong></p> <p>One of the suggestions was to use free functions. I'll show it here as pseudo-code:</p> <pre><code>typedef std::vector&lt;MyObject&gt; MyCollection; void specialCollectionInitializer(MyCollection&amp; c, arguments...); result specialCollectionFunction(const MyCollection&amp; c); etc... </code></pre> <p>A more OO way of doing it:</p> <pre><code>typedef std::vector&lt;MyObject&gt; MyCollection; class MyCollectionWrapper { public: // Constructor MyCollectionWrapper(arguments...) {construct coll_} // Access collection directly MyCollection&amp; collection() {return coll_;} const MyCollection&amp; collection() const {return coll_;} // Special domain-related methods result mySpecialMethod(arguments...); private: MyCollection coll_; // Other domain-specific member variables used // in conjunction with the collection. } </code></pre>
 

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