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c++ lambda without using C++11 [solved]
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DaggyStyle
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PostPosted: Wed Jan 09, 2013 7:53 am    Post subject: c++ lambda without using C++11 [solved] Reply with quote

Hello,

I'm trying write a lambda example program to try and understand it more.
I have the following code:
Code:

#include <boost/lambda/bind.hpp>
#include <iostream>
#include <vector>

template< typename Iterator, typename Callback >
void print1(Iterator start, Iterator end, Callback func)
{
  for (Iterator it = start; it != end; it++)
     func(it);
}

template< typename Iterator >
void print_it(Iterator it)
{
   std::cout << *it << std::endl;
}

int main()
{
  std::vector< int > v;
  for( int i = 1; i < 6; i++)
    v.push_back(i);

  print1< std::vector< int >::iterator >(v.begin(), v.end(), boost::lambda::bind(&print_it, boost::lambda::_1));
  return 0;
}


when I compile it, I get this:
Code:

bltf.cpp: In function ‘int main()’:
bltf.cpp:110:110: error: no matching function for call to ‘bind(<unresolved overloaded function type>, boost::lambda::placeholder1_type&)’
bltf.cpp:110:110: note: candidates are:

as I'm touching lambda for the first time, I'm having hard time to understand what is messing or what I did wrong, can anyone assist me on this matter?

btw, I cannot use C++11 or similar official extensions, I can however use boost.

Thanks.
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Last edited by DaggyStyle on Wed Jan 09, 2013 8:13 am; edited 1 time in total
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aderesch
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PostPosted: Wed Jan 09, 2013 8:03 am    Post subject: Re: c++ lambda without using C++11 Reply with quote

Just looking at it, I'd say you need to instantiate the print_it template for the bind call:
Code:
print_it< std::vector< int >::iterator >


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DaggyStyle
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PostPosted: Wed Jan 09, 2013 8:12 am    Post subject: Reply with quote

right! it worked!

the only replacement I needed is this:
Code:
print1< std::vector< int >::iterator >(v.begin(), v.end(), boost::lambda::bind(&print_it, boost::lambda::_1));

to this:
Code:
print1< std::vector< int >::iterator >(v.begin(), v.end(), boost::lambda::bind(&print_it< std::vector< int >::iterator >, boost::lambda::_1));


I've should have seen it, thanks!
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Hu
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PostPosted: Thu Jan 10, 2013 2:11 am    Post subject: Reply with quote

To clarify, the problem, as reported in the original error message, is that the bare name print_it is ambiguous. If you were calling it at the place it was named, the compiler could use the parameter list to disambiguate. With no parameter list, the function declared as a template, and boost::bind overloaded to accept a variety of function signatures, the compiler is unable to determine the correct type to bind to your typename Iterator. A non-template version of print_it would likely be unambiguous even with a bare name.
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DaggyStyle
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PostPosted: Thu Jan 10, 2013 6:17 am    Post subject: Reply with quote

Hu wrote:
To clarify, the problem, as reported in the original error message, is that the bare name print_it is ambiguous. If you were calling it at the place it was named, the compiler could use the parameter list to disambiguate. With no parameter list, the function declared as a template, and boost::bind overloaded to accept a variety of function signatures, the compiler is unable to determine the correct type to bind to your typename Iterator. A non-template version of print_it would likely be unambiguous even with a bare name.


thanks for clearing it.
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