Re: [Boost-users] problem with boost::any, boost::lambda

25 Sep 2007


      Nat Goodspeed wrote:
...
Fei Liu wrote:
...
using namespace std;
using namespace boost::lambda;
using namespace boost;
using boost::any_cast;
int main(){
vector<any> a;
std::for_each(a.begin, a.end(), if_then(_1.type() == typeid(int))[cout 
<< _1 << ' ']);
}
Invoking a method on a placeholder is a documented limitation:
http://boost.org/doc/html/lambda/le_in_details.html#id1244744
The '.' operator cannot be overloaded. Therefore you must use bind(). 
Because you're using boost::lambda::if_then, I'm sure you're better off 
using boost::lambda::bind than plain boost::bind, though the fact that 
both have been brought into the current namespace makes me think that an 
explicit reference might help -- something like:
boost::lambda::bind(&any::type, _1)
(Disclaimer: I haven't tried to compile your example, with or without my 
suggestion.)
______________________________________
Thank you, unfortunately I am getting even more cryptic error messages 
now after I use explicit bind call:
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

#include 
#include 
#include 
#include 

using namespace std;
using namespace boost::lambda;
using namespace boost;
using boost::any_cast;

int main(){
    vector<any> a;
    any val = 3;
    a.push_back(val);
    val = string("456");
    a.push_back(val);

    std::for_each(a.begin, a.end(), 
if_then(boost::lambda::bind(&any::type, _1) == typeid(int))[cout << _1 
<< ' ']);
}