Re: [Boost-users] [boost-users] anyways to flatten a stl container.

24 Oct 2007


      Digvijoy Chatterjee wrote:
...
...and how do u intend to create a container that stores any container(
set, multiset ,list, vector..... ) in C++ , if u really want stuff
like Ruby ....take a look at boost::variant ( already known types of
containers to store in a container ) , or boost::any ( unknown
container types to be stored in a container )
HTH
Digz
On 10/23/07, chun ping wang  wrote:
...
hmm it could be container of any type (set, multiset, list, vector, array,
deque).
It should act like ruby on rails, flatten.
http://www.ruby-doc.org/core/classes/Array.html#M002241
If you are looking for a function to flatten any STL container [of STL 
containers [etc]], the code below will work.  (It works under VS 2003.) 
    It may need cleaning up, and incorrect usage may generate horrid 
error messages.  There are some test functions at the end.

David

#include <vector>
#include <deque>
#include <list>
#include <cassert>

#include 
#include 
#include 
#include 
#include 

using namespace boost;
using namespace boost::assign;
using namespace std;


template 
struct is_leaf_of_iterator
{
     static const bool value = false;
};


// Normal iterator
template 
struct is_leaf_of_iterator >::type>
{
     static const bool value =
         is_same<
             ContainerObject,
             iterator_traits<OutIt>::value_type
         >::value;
};

// back iterator, front iterator, insert iterator(?)
template 
struct is_leaf_of_iterator >::type>
{
     static const bool value =
         is_same<
             ContainerObject,
             OutIt::container_type::value_type
         >::value;
};


template 
struct do_flatten;

// Call self again with sub-container until reach a leaf.
// A leaf is defined as the type expected by the output iterator.
template 
struct do_flatten
{
     static void apply(const ContainerObject &c, OutIt &out)
     {
         for(ContainerObject::const_iterator it = c.begin() ; it != 
c.end() ; ++it)
         {
             do_flatten::value
             >::apply(*it, out);
         }
     }
};

// partial specialization for non-containers
template 
struct do_flatten
{
     static void apply(const ContainerObject &c, OutIt &out)
     {
         *out = c;
         ++out;
     }
};

template 
void flatten(const ContainerObject &c, OutIt &out)
{
     static const bool isleaf = is_same::value;
     do_flatten::apply(c, out);
}

static std::vector<int> MakeV1_6()
{
     std::vector<int> v; v += 1,2,3,4,5,6; // this uses boost::assign
     return v;
}

static void Test1()
{
     typedef std::deque<int> deque_int;
     typedef std::vector< deque_int > vector_deque_ints;

     deque_int d1; d1 += 1,2,3;
     deque_int d2; d2 += 4,5,6;
     vector_deque_ints v; v += d1,d2; // [[1,2,3],[4,5,6]]

     std::vector<int> out;
     flatten(v, std::back_inserter(out));

     assert(out == MakeV1_6());
}

static void Test2()
{
     typedef std::deque<int> d_i;
     typedef std::list l_d_i;
     typedef std::vector< l_d_i > v_l_d_i;

     d_i d1; d1 += 1,2;
     d_i d2; d2 += 3,4;
     d_i d3;d3 += 5,6;

     l_d_i l1; l1 += d1,d2;
     l_d_i l2; l2 += d3;

     v_l_d_i v; v += l1, l2; //[[[1,2],[3,4]],[[5,6]]]

     std::vector<int> out;
     flatten(v, std::back_inserter(out));

     assert(out == MakeV1_6());
}


int main()
{
     std::vector<int> v;
     v.push_back(0);

     flatten(static_cast<int>(0), v.begin());
     flatten(v, v.begin());

     std::vector<double> d;
     //flatten(d, v.begin()); // fails: v.begin() wrong type for double

     Test1();
     Test2();
}

Re: [Boost-users] [boost-users] anyways to flatten a stl container.

David Walthall