Re: Supply code as template parameter

Thu, 6 Nov 2008 23:07:46 CST
On Nov 5, 11:13 pm, "Edward Jensen" <edw...@jensen.invalid> wrote:


I need to write many instances like the following struct

struct Function191 : public Function {
     double operator()(double x) {
         return cos(x) - x;
     friend std::ostream& operator<< (std::ostream& os, const Function191&

f) {

         return os << "cos(x) - x";


Is there a way to generalize this, such that I can write a generic


struct, which takes a parameter which is both interpreted as code for
operator() and as string for operator<<? I was hoping it would be possible
with templates for example:
struct<"cos(x) - x">Func f1;
struct<"exp(x) - log(x)">Func f2;

Is this possible?


  Without using the preprocessor, an interpreter, or a special code
generator, I can't think of a way to do this.
   The preprocessor approach might work for simple
cases but like one line functions of x which don't contain comma's.
   struct Function
     virtual double exec(double)const = 0;
     virtual const char *name() const = 0;
     double operator () (double x) {return exec(x);}

#define MAKE_FUNCTION(f_name,body)\
struct f_name:Function\
   double exec(x)const { return body;}\
   const char *name() { return #f_name;}\


is a quick solution.

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