Question

We have written a large library functions whose prototypes mostly look like:

void my_fun(
  const in_class & in_param_1, 
  const in_class & in_param_2,
  const in_class & in_param_3,
  out_class & out_param);

Is there a generic way to wrap these functions so that the following is equivalent (assuming out_param is only written to in my_fun):

out_class my_out;
my_fun(my_in1,my_in2,my_in3,my_out);

and

out_class my_out = generic_wrapper(&my_fun,my_in1,my_in2,my_in3);

How could one write such a generic_wrapper? If this is possible it also possible to write it so that the number of input parameters is variable, so I could use it say with my_fun2 that perhaps takes 4 in_param_’s?

Answer 1

Consider all cases:

template<class T1, class Out>
Out generic_wrapper(void (*f)(const T1 &, Out &), const T1 & t1) { 
    Out out; 
    f(t1,out); 
    return out;
}

template<class T1, class T2, class Out>
Out generic_wrapper(void (*f)(const T1 &, const T2 &, Out &), const T1 & t1, const T1 & t2) { 
    Out out; 
    f(t1,t2,out); 
    return out;
}

// .....

template<class T1, class T2, class T3, class T4, class T5, class Out>
Out generic_wrapper(void (*f)(const T1 &, const T2 &, const T3 &, const T4 &, const T5 &, Out &), const T1 & t1, const T1 & t2, const T3 & t3, const T4 & t4, const T5 & t5) { 
    Out out; 
    f(t1,t2,t3,t4,t5,out); 
    return out;
}