50b4b57b   
   From: daniel.kruegler@googlemail.com   
      
   Am 08.03.2012 21:44, schrieb Quint Rankid:   
   > On Mar 6, 4:18 pm, "Jimmy H."  wrote:   
   >   
   >> #include   
   >> #include   
   >>   
   >> template   
   >> auto operator*(std::function  a, std::function  b) ->   
   >>      std::function   
   >> {   
   >>      return [a,b](C c) { return a(b(c)); };   
   >>   
   >> }   
   >>   
   >> int addOne(int a) {   
   >>      return a + 1;   
   >>   
   >> }   
   >>   
   >> int main() {   
   >>      std::function  addOneFunc(addOne);   
   >>      std::cout<<  (addOneFunc * addOneFunc)(2)<<  std::endl;   
   >>   
   >> }   
   >>   
   >> Notably, though, I need to explicitly convert addOne to a   
   >> std::function for it to call the custom operator* function. Attempting   
   >> to write a helper template to do the conversion for me:   
   >   
   > I don't understand.   
   >   
   > The above code seems to compile and run using GNU C++ (GCC) version   
   > 4.6.1 (mingw32).  I used the -std=c++0x command line argument.   
   >   
   > I think that you are using a compiler that doesn't support this, or I   
   > don't understand what you are trying to accomplish.  Can you please   
   > say what compiler you are using and expand on the need to explicitly   
   > convert addOne.   
      
   No, you are misunderstanding the OP here (I also needed a while to   
   understand the request): He described that above construction works, his   
   complain was that instead of above shown expression   
      
   (addOneFunc * addOneFunc)(2)   
      
   the simpler one   
      
   (addOneFunc * addOne)(2)   
      
   using the function addOne directly as operand does not compile. This is   
   so, because argument conversions are (usually) not considered for   
   function templates. One of the rare exceptions are function-to-pointer   
   and array-to-pointer conversions when the template parameter is not a   
   reference type (see [temp.deduct.call] p2).   
      
   HTH & Greetings from Bremen,   
      
   Daniel Krügler   
      
      
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