[Bug c++/52185] New: Const member function may change the object for which the function is called.

["lsoltysiak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52185

             Bug #: 52185
           Summary: Const member function may change the object for which
                    the function is called.
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: lsoltysiak@gmail.com


According to paper www.open-std.org/JTC1/SC22/WG21/docs/papers/2011/n3242.pdf (
class.this point 2), a const member function shall not modify the object for
which the function is called.

With basic cases it is true, so for below class g++ returns error ('error:
increment of member âA::aâ in read-only object').

class A {
    int a;
    public: int fun() const { a++; }
};

Problems start when class contains references. In below example, const member
function allows to change internal state of class A instances. This shouldn't
be allowed. In my opinion compilation should failed, but g++ 4.7.0 doesn't
report any problem.

class A {
    int   a1;
    int & a2;
  public: 
    A() : a2(a1) { }
    int fun() const { a2++; }
};