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POHow do I remove code duplication between similar const and non-const member functions in abstract classes?
 

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  1. POHow do I remove code duplication between similar const and non-const member functions in abstract classes?
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    <p>first of, this is a follow up question to this one: <a href="https://stackoverflow.com/questions/123758/how-do-i-remove-code-duplication-between-similar-const-and-non-const-member-func?rq=1">How do I remove code duplication between similar const and non-const member functions?</a></p> <p>Let's say, I have an abstract class, providing one pure virtual function:</p> <pre><code>class ICommand { public: virtual ~ICommand() {}; virtual int Execute() = 0; protected: ICommand() {}; };//class ICommand </code></pre> <p>And another class inheriting from this one:</p> <pre><code>class cCommand : public ICommand { public: cCommand() {}; virtual ~cCommand() {}; virtual int Execute() { int retval = 0; //do something and return appropriate error code return retval; } };//class cCommand </code></pre> <p>Now I need a pointer to an object of type ICommand, but with const data, like:</p> <pre><code>//using a smart pointer here would be better, but it shows the problem ICommand const * p = new cCommand(); int retval = p-&gt;Execute(); //won't compile </code></pre> <p>The problem is, I call a non const member function on a const object. So i either have to remove the const when creating pointer p (bad, I guess...) or I have to add a const member function Execute() to ICommand as well. After struggeling a little with the fact, that the user has to implement two functions than (not to mention what happens, if we add some other pure virtual functions to the base class...), I came up with the following solution:</p> <pre><code>class ICommand { public: virtual ~ICommand() {}; virtual int Execute() { //Scott Meyers way return static_cast&lt;const ICommand&amp;&gt;(*this).Execute(); } virtual int Execute() const = 0; protected: ICommand() {}; };//class ICommand </code></pre> <p>That seems to do the job quite well, but I'm not sure whether this a suitable solution to my problem. Neither I think this is very intuitive for the user as he always has to implement the const version of the pure virtual member function, but not the non const one.</p> <p>My actual question is, whether there are any side effects I might not have considered or if there is any better solution to this problem I might have overseen so far.</p> <p>Thanks in advance, René.</p>
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