Re: substituting a function ptr with a function object

Barry <>
Sat, 22 Sep 2007 13:28:17 +0800
er wrote:


class Gen{
        Gen(double (*fun_)()):fun(fun_){};
        double (*fun)();
class Op{
        double operator()(){return 0.0;};
double fun(){return 0.0;};

// i'd like to be able to construct Gen from either a fun ptr (OK,
fine as is) or a function object. the code below is probably
adventurous...any suggestion?

int main(){
    Gen gen1(&fun);//ok
    Op op;
    Gen gen2(
    );//error: no matching function for call.//the result from bind does
not match double (*)()


returns is not typeof "double (*fun_)()",
it's functor.

As Erik mentioned else thread, using template, but it's a solution
you don't even know the how to fill T in Gen<T>;

Stop reinventing another wheel, have a look at Boost.Function first,
use it, or refer to it, and write something exactly meets your need

In your case, you can use boost::function0<double> (equivalent to
boost::function<double()>) as your functor/function wrapper,
you can then use boost::bind to bind any function/functor who returns
double, or you can even write some adapter.

#include <boost/bind.hpp>
#include <boost/function.hpp>

#include <functional>

double fun() { return 0.0; }

struct Adapter
     : std::unary_function<double, int>
     double operator() (int) { return 0.0; }

int getint(char c) { return 0; }

int main()
     boost::function0<double> f = &fun;
     double d = f();

     f = boost::bind(Adapter(), boost::bind(&getint, 10));
     d = f();


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