Re: [Boost-users] [bind] How do I....?

Subject: Re: [Boost-users] [bind] How do I....?
From: Björn Karlsson (Bjorn.Karlsson_at_[hidden])
Date: 2009-08-18 05:46:52

Hello Rob,

> Subject: [Boost-users] [bind] How do I....?
> 
> Use bind to call a free function on a vector of shared_ptrs?
> 
> struct A { };
> void f(const A&);
> std::vector<boost::shared_ptr<A> > v;
> 
> for_each(v.begin(), v.end(), boost::bind(f, ???? ) );
> 
> what goes where ???? is?
> 

You have two options if you want to use binders: 

1) Use Boost.Bind with nested binds, binding operator* of shared_ptr in the inner bind. 

  for_each(vec.begin(), vec.end(), boost::bind(&foo, boost::bind(&boost::shared_ptr<A>::operator*, _1)));

2) Use Boost.Lambda's bind() and dereference the placeholder directly in the bind expression.

  for_each(vec.begin(), vec.end(), bind(&foo, *_1));

Here's a complete example demonstrating option 2).

#include <vector>
#include <algorithm>
#include "boost/shared_ptr.hpp"

#include "boost/lambda/bind.hpp"
#include "boost/lambda/lambda.hpp"

class A {};

void foo(const A& a) {}

int main(int argc, char** argv)
{
  using boost::lambda::bind;
  using boost::lambda::_1;

  std::vector<boost::shared_ptr<A> > vec;
  vec.push_back(boost::shared_ptr<A>(new A()));

  for_each(vec.begin(), vec.end(), bind(&foo, *_1));

  return 0;
}

Cheers,
Bjorn Karlsson
www.skeletonsoftware.net