[Bug libstdc++/43595] New: std::unique incorrectly assumes transitive property on functor, operator==

[potswa at mac dot com]

According to the standard §25.2.8, std::unique has behavior defined in terms of

   *i == *(i - 1) or pred(*i, *(i - 1)) != false

however the current implementation compares each successive element to the
first in the "equal" range. This is only equivalent if the transitive property
holds.

This is certainly wrong if a functor is passed, and it may be wrong for the
other case as well. The non-functor version is defined to evaluate *i == *(i -
1) but does not require EqualityComparable elements.

C++0x does impose this requirement: "The comparison function shall be an
equivalence relation."


-- 
           Summary: std::unique incorrectly assumes transitive property on
                    functor, operator==
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: potswa at mac dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43595