Question

boost::algorithm::join provides a convenient join on std::vector<std::string>.

How would you expand this functionality to use std::vector<std::tuple<std::string,bool>> to surround the results with single-quotes (for strings) if true, before doing the join.

This is not hard to do with loops, but I am looking for a solution that makes the most use of standard algorithms and C++11 features (eg lambdas).

Continue to use boost’s join, if feasible: elegance/readability/conciseness are more important.

CODE

#include <string>
#include <vector>
#include <tuple>
#include <boost/algorithm/string/join.hpp> 

int main( int argc, char* argv[] )
{
  std::vector<std::string> fields = { "foo", "bar", "baz" };
  auto simple_case = boost::algorithm::join( fields, "|" );

  // TODO join surrounded by single-quotes if std::get<1>()==true
  std::vector<std::tuple< std::string, bool >> tuples =
   { { "42", false }, { "foo", true }, { "3.14159", false } };

  // 42|'foo'|3.14159 is our goal
}

EDIT

OK, I took kassak’s suggestion below and took a look at boost::transform_iterator() – I got put off by the verbosity of the example in boost’s own documentation, so I tried std::transform() – it’s not as short as I wanted, but it seems to work.

ANSWER

#include <string>
#include <vector>
#include <tuple>
#include <iostream>
#include <algorithm>
#include <boost/algorithm/string/join.hpp> 

static std::string
quoted_join( 
    const std::vector<std::tuple< std::string, bool >>& tuples, 
    const std::string& join
)
{
    std::vector< std::string >  quoted;
    quoted.resize( tuples.size() );
    std::transform( tuples.begin(), tuples.end(), quoted.begin(),
        []( std::tuple< std::string, bool > const& t ) 
        {
            return std::get<1>( t ) ? 
                "'" + std::get<0>(t) + "'" :
                std::get<0>(t);
        }
    );
  return boost::algorithm::join( quoted, join );
}

int main( int argc, char* argv[] )
{
  std::vector<std::tuple< std::string, bool >> tuples =
  { 
    std::make_tuple( "42", false ), 
    std::make_tuple( "foo", true ), 
    std::make_tuple( "3.14159", false ) 
  };

  std::cerr << quoted_join( tuples, "|" ) << std::endl;
}

Answer 1

If you want to use join, you could wrap collection in boost::transform_iterator and add quotes if needed