Re: [Boost-users] boost::ref and boost:::function

12 Mar 2007

      Hi!

the std::find_if function takes as it's third parameter an unary predicate function or function
object which evaluates the condition.

To implement this you can write your comparison function looking like:

template<class FunctionType>
struct compare_functions
{
  compare_functions(FunctionType f) : func_(f)
  {}

  template<class RefObj>
  bool operator()(RefObj r)const
  {
     return func_==r; //boost::reference_wrapper<T> has an operator T& which is called implicitly
  }

private:
    FunctionType    func_;
};

modifications in your code:
void remove(boost::function<void (int v)> fun)
{
    std::list<boost::function<void (int v)> >::iterator iter;

    //IMPLEMENTATION
    std::find_if(fun_list.begin(), fun_list.end(), compare_functions(fun));

    if(iter != fun_list.end())
      fun_list.erase(iter);
}

You could also skip the compare_functions implementation and use boost::lambda and placeholder
library to write you code like this:
    std::find_if(fun_list.begin(), fun_list.end(), _1==fun);

With Kind Regards,

Ovanes Markarian

On Mon, March 12, 2007 09:48, misiu wrote:
...
Hello,
Could you please tell me how to compare two boost::function objects
packet with boost::ref. I have container which has boost::function
elements and to add elements is not a problem but to remove particular
one I don't know how to do that (compare two boost:ref-s). The problem
is shown in the code below.
Regards,
Bartek
//code
#include <iostream>
#include <list>
#include <boost/ref.hpp>
#include <boost/function.hpp>
struct test{
   int a;
   void operator() (int aa)
   {  a += aa; }
};
struct function_list {
   std::list<boost::function<void (int v)> > fun_list;
void add(boost::function<void (int v)> fun)
   {
     fun_list.push_back(fun);
   }
void remove(boost::function<void (int v)> fun)
   {
     std::list<boost::function<void (int v)> >::iterator iter;
//HOW TO IMPLEMETN THIS FIND_IF?
     //std::find_if(fun_list.begin(), fun_list.end(), MISSING_PART);
if(iter != fun_list.end())
       fun_list.erase(iter);
   }
};
int main(int argc, char **argv) {
test a, b;
   function_list f;
f.add(boost::ref(a));
   f.add(boost::ref(b));
   //DOES NOT WORK
   f.remove(boost::ref(a));
}
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