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POHow to store an "object type" in a std::map?
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copied!<p>Long introduction, question is at the end:</p> <hr> <p>Assume I have a base class that's creating an interface</p> <pre><code>class base { public: virtual ~base(); virtual void calc( int* variables ) = 0; } </code></pre> <p>and a few classes that are inherited that do the work (only two are shown here):</p> <pre><code>class add : public base { const int a, b, c; public: add( int a_, int b_, int c_ ) : a(a_), b(b_), c(c_) {} void calc( int* variables ) { variables[a] = variables[b] + variables[c]; } } class inc : public base { const int a; public: inc( int a_ ) : a(a_) {} void calc( int* variables ) { variables[a]++; } } </code></pre> <p>and finally some code that's using this construct:</p> <pre><code>base* task[2]; task[0] = new add( 0, 1, 2 ); task[1] = new inc( 3 ); int data[4]; /* ... */ for( int i = 0; i < 2; i++ ) task[i]->calc( data ); </code></pre> <p>That's working so far - but it's defining my tasks during compile time. This should be changed to runtime by parsing an input file. Assume the parsing has been done and in <code>std::string</code> variable <code>command</code> is the object type (like <code>add</code> or <code>inc</code>) and in a <code>std::vector<int> params</code> are the parameters for the constructor.</p> <p>Now I could have a long list of</p> <pre><code>if( command.compare( "add" ) ) task[end] = new add( params[0], params[1], params[2] ); else if( command.compare( "inc" ) ) task[end] = new inc( params[0] ); else /... */ </code></pre> <p>apart from becoming quite unreadable that's just a linear seach. So in the spirit of <a href="https://stackoverflow.com/questions/650162/why-switch-statement-cannot-be-applied-on-strings">Why switch statement cannot be applied on strings?</a> I'd like to replace that linear search by a <code>std::map</code> (or hash map...).</p> <p>So after this long introduction I can finally come to the question:</p> <hr> <p><strong>How can I define and fill a <code>std::map</code> so that references(?) to an object are stored in such a way that I can create late on the object dynamically out of that informations?</strong></p> <p>So with the code above I'd like to do something that might look like this in the end:</p> <pre><code>// define and fill std::map< std::sting, ???? > lookup; lookup["add"] = add; lookup["inc"] = inc; /* ... */ // use: while( linesInConfigAvailable ) { /* ... parse ... */ switch( params.size() ) { case 1: task[end] = new lookup[command]( params[0] ); break; case 3: task[end] = new lookup[command]( params[0], params[1], params[2] ); break; } } </code></pre> <p>PS: So far I didn't need RTTI in my code. It'd be nice if that could stay so...</p>

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