[Boost-bugs] [Boost C++ Libraries] #9515: [range] uniqued adaptor (and hence adjacent_filtered) returns wrong elements

Subject: [Boost-bugs] [Boost C++ Libraries] #9515: [range] uniqued adaptor (and hence adjacent_filtered) returns wrong elements
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-12-20 22:10:53

#9515: [range] uniqued adaptor (and hence adjacent_filtered) returns wrong
elements
------------------------------+---------------------
 Reporter:  eric_niebler      |      Owner:
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  None
  Version:  Boost 1.54.0      |   Severity:  Problem
 Keywords:                    |
------------------------------+---------------------
 The following shows the difference between the `boost::range::unique_copy`
 algorithm and the `boost::adaptors::unique` adaptor.

 {{{
 #include <string>
 #include <vector>
 #include <iterator>
 #include <iostream>
 #include <boost/algorithm/string.hpp>
 #include <boost/range/algorithm/copy.hpp>
 #include <boost/range/algorithm/unique_copy.hpp>
 #include <boost/range/adaptor/uniqued.hpp>

 struct istring
 {
     char const *c_str;
     istring(char const *s) : c_str(s) {}
     bool operator==(istring u) const
     {
         return boost::iequals(c_str, u.c_str);
     }
     friend std::ostream& operator<<(std::ostream& sout, istring s)
     {
         return sout << s.c_str;
     }
 };

 int main()
 {
     std::vector<istring> strs;
     strs.push_back(istring("hello"));
     strs.push_back(istring("HELLO"));
     std::cout << "boost.range: \n";
     boost::range::copy(
         boost::adaptors::unique(strs),
         std::ostream_iterator<istring>(std::cout));

     std::cout << "\n";
     std::cout << "std algo: \n";
     boost::range::unique_copy(strs,
         std::ostream_iterator<istring>(std::cout));
     std::cout << "\n";
 }
 }}}

 This prints:

 {{{
 boost.range:
 HELLO
 std algo:
 hello
 }}}

 `std::unique` and `std::unique_copy` yield the *first* element in a
 sequence of equivalent elements. The Boost adaptor yields the last. This
 is an important and observable difference.

 Since `uniqued` is implemented in terms of `adjacent_filtered`, the
 problem needs to be fixed there.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/9515>
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