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POIs it possible to defer the generation of a functor?
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copied!<p>I had an interesting idea of creating a type of vector table using functors. However, after further analysis it would seem that this would be a pipe dream due to the fact that it would be prohibitively expensive since the <em>entire</em> table would have to be generated to pass on some of the function parameters from the function that calls the functor. The functor in this case would act as a proxy to manage parameter differences between functions that the functor is calling.</p> <p>Confused yet? :-) Example:</p> <pre><code>#include <functional> class classA {}; void fn1(int a); void fn2(classA& a); void fn_x(int fn_to_call, int a1, classA& a2) { std::function<void()> vtable[] = { [&]{ fn1(a1); }, [&]{ fn2(a2); } }; vtable[fn_to_call](); } void fn_y(int fn_to_call, int a1, classA& a2) { switch(fn_to_call) { case 0: return fn1(a1); case 1: return fn2(a2); } } </code></pre> <p>For brevity, I skipped checks as I'm doing this on a phone.</p> <p>So as I understand it, fn_x would have to create an array of functors upon entering the function, and then call the one required. Whereas fn_y would just jump to the one required.</p> <p>When the number of functions to dispatch is small, this isn't much of a problem, but as the number increases, it becomes worse and worse.</p> <p>If I could somehow defer the creation of the functor objects until it it's called, that would be optimal. Is that possible?</p> <p><strong>Edit</strong> also, how will a compiler handle this? Will it result in multiple calls stack entries (a call to the functor and then a call to the target function) or would it just be as efficient as the switch?</p>

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