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Passing a boost::unordered_set as the result map to boost::split

Answer 1

A:

Apparently, the answer is no yes.

Using the following code, I get compile-time warnings and a runtime assert (Visual C++ v10) on the unordered_set while the vector works fine (apart from an empty string in the last element, due to the trailing '^').

boost::unordered_set<std::string> tags_set;
vector<string> SplitVec; // #2: Search for tokens
boost::split( SplitVec, "a^b^c^", boost::is_any_of("^") ); 
boost::split( tags_set, "a^b^c^", boost::is_any_of("^") );

Iterator compatibility between source (string) and the target container is the issue. I would post the warning error, but it's one of those "War and Peace" template warnings.

EDIT:

This looks like a bug in Boost unordered_set? When I use the following, it works as you would expect:

std::unordered_set<std::string> tags_set_std;
boost::split( tags_set_std, string("a^b^c^"), boost::is_any_of(string("^")) );

Steve Townsend 2010-10-20 19:30:05

Thanks Steve. What version of boost are you using?

Jeremy Stribling 2010-10-20 19:39:51

@Jeremy - 1.44.0

Steve Townsend 2010-10-20 19:50:54

@Jeremy - see EDIT

Steve Townsend 2010-10-20 20:59:51

Answer 2

A:

I think the answer should be yes.

Reading the headers (split.hpp and iter_find.hpp) split takes a SequenceSequenceT& Result as its first argument, which it passes to iter_split which range-constructs it from two boost::transform_iterators:

SequenceSequenceT Tmp(itBegin, itEnd);
Result.swap(Tmp);
return Result;

So all it needs of this type is that it has a constructor that takes a pair of iterators which dereference to std::string (or, technically, to BOOST_STRING_TYPENAME). And has a .swap() member.. and has a SequenceSequenceT::iterator type whose type is std::string.

proof:

#include <boost/algorithm/string/classification.hpp>
#include <boost/algorithm/string/split.hpp>
#include <string>
#include <iterator>
#include <algorithm>
#include <iostream>
struct X
{
   typedef std::iterator<std::forward_iterator_tag,
           std::string, ptrdiff_t, std::string*, std::string&>
           iterator;
   X() {}
   template<typename Iter> X(Iter i1, Iter i2)
   {
       std::cout << "Constructed X: ";
       copy(i1, i2, std::ostream_iterator<std::string>(std::cout, " " ));
       std::cout << "\n";
   }
   void swap(X&) {}
};
int main()
{
  X x;
  boost::split(x, "a^b^c^", boost::is_any_of(std::string(1, '^')));
}

I think that unordered_set<std::string> should satisfy these requirements as well.

Cubbi 2010-10-20 19:55:50

Thanks @Cubbi. So your conclusion is that this is a bug somewhere in Boost 1.42, and that the compiler warnings seen by @Steve on VisualC++/boost 1.44 are misleading?

Jeremy Stribling 2010-10-20 20:37:35

@Jeremy Stribling: It's what I would expect, seeing how my test and gcc's unordered_set work where boost's doesn't, but they might have had a good reason. I'd wait for more answers here and test more before calling it a bug.

Cubbi 2010-10-20 21:01:31

@Jeremy - see edit, I got this working with `std::unordered_set` instead of `boost::unordered_set`

Steve Townsend 2010-10-20 21:02:12

Answer 3

+1 A:

This was confirmed on the boost-users mailing list to be a bug in the boost::unordered_set implementation. There is a patch available on the mailing list, and a fix will be checked in soon, hopefully in time for boost 1.45.

Boost-users: patch

Boost-users: confirmation

Thanks everyone for looking into this!

Jeremy Stribling 2010-10-21 17:29:50

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Passing a boost::unordered_set as the result map to boost::split

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