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2

1

This code was inspired by another question on Stack Overflow a few days ago. It attempts to use a transform iterator to construct a std::vector containing a non-movable type.

#include <cstdio>
#include <iterator>
#include <vector>

#define BOOST_RESULT_OF_USE_DECLTYPE
#include <boost/iterator/transform_iterator.hpp>

struct NonMovable 
 NonMovable(const NonMovable&) = delete;
 void operator=(const NonMovable&) = delete;
 NonMovable(NonMovable&&) = delete; // redundant
 void operator=(NonMovable&&) = delete; // redundant
 NonMovable(int x, int y) : x(x), y(y) 
 int x;
 int y;
;

int main(int argc, char* argv[])

 std::vector<int> args = 1, 2, 3, 4;
 int additional_arg = 5;
 auto fun = [&additional_arg](auto arg) return NonMovable(arg, additional_arg); ;
 std::vector<NonMovable> v(boost::make_transform_iterator(args.begin(), fun),
 boost::make_transform_iterator(args.end(), fun));
 for (const auto& item : v) 
 printf("%d %dn", item.x, item.y);
 

Unfortunately, this code doesn't compile (https://wandbox.org/permlink/20xMUsCBUg44YmXC). The error message from Clang mentions that the std::vector range constructor is disabled because:

no type named 'reference' in 'std::__1::iterator_traits<boost::iterators::transform_iterator<(lambda at prog.cc:22:16), std::__1::__wrap_iter<int *>, boost::iterators::use_default, boost::iterators::use_default> >'

But I can't see any reason why this iterator_traits specialization should not have a member named reference.

c++ iterator boost-iterators

share|improve this question

asked Mar 8 at 18:48

BrianBrian

66.8k799191

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Not movable, not copyable, nor assignable, I wouldn't expect vector to work with it either
  
  – JVApen
  Mar 8 at 18:52
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  See stackoverflow.com/questions/54953039/…
  
  – R2RT
  Mar 8 at 20:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Could it be: github.com/llvm-mirror/libcxx/blob/master/include/iterator#L491 ?
  
  – Jeff Garrett
  Mar 8 at 20:30
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It seems make_transform_iterator requires fun to be assignable. How can that be? A lambda is never assignable right?
  
  – rustyx
  Mar 8 at 21:51
  

  
  
  
  

add a comment | 

2

1

This code was inspired by another question on Stack Overflow a few days ago. It attempts to use a transform iterator to construct a std::vector containing a non-movable type.

#include <cstdio>
#include <iterator>
#include <vector>

#define BOOST_RESULT_OF_USE_DECLTYPE
#include <boost/iterator/transform_iterator.hpp>

struct NonMovable 
 NonMovable(const NonMovable&) = delete;
 void operator=(const NonMovable&) = delete;
 NonMovable(NonMovable&&) = delete; // redundant
 void operator=(NonMovable&&) = delete; // redundant
 NonMovable(int x, int y) : x(x), y(y) 
 int x;
 int y;
;

int main(int argc, char* argv[])

 std::vector<int> args = 1, 2, 3, 4;
 int additional_arg = 5;
 auto fun = [&additional_arg](auto arg) return NonMovable(arg, additional_arg); ;
 std::vector<NonMovable> v(boost::make_transform_iterator(args.begin(), fun),
 boost::make_transform_iterator(args.end(), fun));
 for (const auto& item : v) 
 printf("%d %dn", item.x, item.y);
 

Unfortunately, this code doesn't compile (https://wandbox.org/permlink/20xMUsCBUg44YmXC). The error message from Clang mentions that the std::vector range constructor is disabled because:

no type named 'reference' in 'std::__1::iterator_traits<boost::iterators::transform_iterator<(lambda at prog.cc:22:16), std::__1::__wrap_iter<int *>, boost::iterators::use_default, boost::iterators::use_default> >'

But I can't see any reason why this iterator_traits specialization should not have a member named reference.

c++ iterator boost-iterators

share|improve this question

asked Mar 8 at 18:48

BrianBrian

66.8k799191

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Not movable, not copyable, nor assignable, I wouldn't expect vector to work with it either
  
  – JVApen
  Mar 8 at 18:52
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  See stackoverflow.com/questions/54953039/…
  
  – R2RT
  Mar 8 at 20:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Could it be: github.com/llvm-mirror/libcxx/blob/master/include/iterator#L491 ?
  
  – Jeff Garrett
  Mar 8 at 20:30
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It seems make_transform_iterator requires fun to be assignable. How can that be? A lambda is never assignable right?
  
  – rustyx
  Mar 8 at 21:51
  

  
  
  
  

add a comment | 

This code was inspired by another question on Stack Overflow a few days ago. It attempts to use a transform iterator to construct a std::vector containing a non-movable type.

#include <cstdio>
#include <iterator>
#include <vector>

#define BOOST_RESULT_OF_USE_DECLTYPE
#include <boost/iterator/transform_iterator.hpp>

struct NonMovable 
 NonMovable(const NonMovable&) = delete;
 void operator=(const NonMovable&) = delete;
 NonMovable(NonMovable&&) = delete; // redundant
 void operator=(NonMovable&&) = delete; // redundant
 NonMovable(int x, int y) : x(x), y(y) 
 int x;
 int y;
;

int main(int argc, char* argv[])

 std::vector<int> args = 1, 2, 3, 4;
 int additional_arg = 5;
 auto fun = [&additional_arg](auto arg) return NonMovable(arg, additional_arg); ;
 std::vector<NonMovable> v(boost::make_transform_iterator(args.begin(), fun),
 boost::make_transform_iterator(args.end(), fun));
 for (const auto& item : v) 
 printf("%d %dn", item.x, item.y);
 

Unfortunately, this code doesn't compile (https://wandbox.org/permlink/20xMUsCBUg44YmXC). The error message from Clang mentions that the std::vector range constructor is disabled because:

no type named 'reference' in 'std::__1::iterator_traits<boost::iterators::transform_iterator<(lambda at prog.cc:22:16), std::__1::__wrap_iter<int *>, boost::iterators::use_default, boost::iterators::use_default> >'

But I can't see any reason why this iterator_traits specialization should not have a member named reference.

c++ iterator boost-iterators

share|improve this question

asked Mar 8 at 18:48

BrianBrian

66.8k799191

#include <cstdio>
#include <iterator>
#include <vector>

#define BOOST_RESULT_OF_USE_DECLTYPE
#include <boost/iterator/transform_iterator.hpp>

struct NonMovable 
 NonMovable(const NonMovable&) = delete;
 void operator=(const NonMovable&) = delete;
 NonMovable(NonMovable&&) = delete; // redundant
 void operator=(NonMovable&&) = delete; // redundant
 NonMovable(int x, int y) : x(x), y(y) 
 int x;
 int y;
;

int main(int argc, char* argv[])

 std::vector<int> args = 1, 2, 3, 4;
 int additional_arg = 5;
 auto fun = [&additional_arg](auto arg) return NonMovable(arg, additional_arg); ;
 std::vector<NonMovable> v(boost::make_transform_iterator(args.begin(), fun),
 boost::make_transform_iterator(args.end(), fun));
 for (const auto& item : v) 
 printf("%d %dn", item.x, item.y);
 

share|improve this question

asked Mar 8 at 18:48

BrianBrian

66.8k799191

share|improve this question

asked Mar 8 at 18:48

BrianBrian

66.8k799191

asked Mar 8 at 18:48

BrianBrian

66.8k799191

asked Mar 8 at 18:48

BrianBrian

66.8k799191