[Boost-users] member data pointer and nested bind

From: JaeWook Choi (zzzz.ooo_at_[hidden])
Date: 2006-02-18 01:16:08

Hello,

I've been trying to use STL alogorithms on POD struct data member without 
writing any user defined functor nor adding get/set member function to the 
POD sturct, instead I just wanted to use boost::mem_fn, boost::bind, 
boost::lambda for member data pointer.

It was fine to use the member data pointer with any of boost::mem_fn, 
boost::bind and boost::lambda only until I tried to use them in the nested 
bind as an argument of outter bind. If I use them in nested bind, I got 
compile error message of "cannot convert parameter 1 from 
'boost::_bi::bind_t<R,F,L> ' to 'const RECT *'" or "cannot convert parameter 
1 from 'boost::lambda::lambda_functor<T>' to 'const RECT *'"

As a boost newbie, it is too difficult for me to figure out the problem 
here. Maybe someone can help me out to sovle the problem.

Thanks,

Jae.

The below is my test code. (BTW, I compiled it on VC71)

~~~

#include "stdafx.h"
#include <wtypes.h>

#include <vector>
#include <algorithm>

using std::vector;
using std::find_if;

#define  BOOST_BIND_ENABLE_STDCALL
#include <boost/bind.hpp>
#include <boost/lambda/lambda.hpp>

using boost::mem_fn;
using boost::bind;

// an arbitrary POD struct
struct CTestClass
{
  RECT rc;
};

int main(int argc, char* argv[])
{
  vector<CTestClass> vecTestClass;

  CTestClass testObj = { { 0, 0, 100, 100} };
  vecTestClass.push_back(testObj);

  ::OffsetRect(&testObj.rc, 100, 100);
  vecTestClass.push_back(testObj);

  LONG rc_left = mem_fn(&CTestClass::rc)(testObj).left;  // mem_data_ptr & 
boost::mem_fn
  LONG rc_top = bind(&CTestClass::rc, _1)(testObj).top;  // mem_data_ptr & 
boost::bind
  LONG rc_right = ((&boost::lambda::_1)->*&CTestClass::rc)(testObj).right; 
// mem_data_ptr & boost::lambda

  POINT ptTest = { 150, 150 };

  ::PtInRect(&mem_fn(&CTestClass::rc)(testObj), ptTest);    // ok
  ::PtInRect(&bind(&CTestClass::rc, _1)(testObj), ptTest);    // ok
  ::PtInRect(&((&boost::lambda::_1)->*&CTestClass::rc)(testObj), ptTest); 
// ok

  vector<CTestClass>::iterator it_f1 =
    find_if(vecTestClass.begin(), vecTestClass.end(),
    bind(::PtInRect, &bind(&CTestClass::rc, _1), ptTest) );    // compile 
error!

  vector<CTestClass>::iterator it_f2 =
    find_if(vecTestClass.begin(), vecTestClass.end(),
    bind(::PtInRect, &((&boost::lambda::_1)->*&CTestClass::rc), ptTest) ); 
// compile error!

  return 0;
}

~~~