[Bug libstdc++/25306] New: fill_n, generate_n assume Size is modifiable

[sebor at roguewave dot com]

I came across this while gathering background for my post in c++std-lib-16112.
I thgought I might as well let you know in case you think it's important enough
to worry about (Size is only required to be convertible to an integral type
which doesn't mean it needs to have the predecrement operator defined). The
incorrect return type in this test case works around bug #25304.

$ cat t.cpp && g++ -c t.cpp
#include <algorithm>

struct Size {
    operator int() { return 0; }
private:
    void operator=(Size&);
};

template int* std::fill_n (int*, Size, const int&);
template int* std::generate_n (int*, Size, int (*)());

int main () { }

/usr/local/gcc-4.0.2/lib/gcc/sparc-sun-solaris2.9/4.0.2/../../../../include/c++/4.0.2/bits/stl_algo.h:
In function '_OutputIterator std::generate_n(_OutputIterator, _Size,
_Generator) [with _OutputIterator = int*, _Size = Size, _Generator = int
(*)()]':
t.cpp:10:   instantiated from here
/usr/local/gcc-4.0.2/lib/gcc/sparc-sun-solaris2.9/4.0.2/../../../../include/c++/4.0.2/bits/stl_algo.h:1003:
error: no match for 'operator--' in '--__n'
/usr/local/gcc-4.0.2/lib/gcc/sparc-sun-solaris2.9/4.0.2/../../../../include/c++/4.0.2/bits/stl_algobase.h:
In static member function 'static _OutputIterator
std::__fill_n<true>::fill_n(_OutputIterator, _Size, const _Tp&) [with
_OutputIterator = int*, _Size = Size, _Tp = int]':
/usr/local/gcc-4.0.2/lib/gcc/sparc-sun-solaris2.9/4.0.2/../../../../include/c++/4.0.2/bits/stl_algobase.h:642:
  instantiated from '_OutputIterator std::fill_n(_OutputIterator, _Size, const
_Tp&) [with _OutputIterator = int*, _Size = Size, _Tp = int]'
t.cpp:9:   instantiated from here
/usr/local/gcc-4.0.2/lib/gcc/sparc-sun-solaris2.9/4.0.2/../../../../include/c++/4.0.2/bits/stl_algobase.h:617:
error: no match for 'operator--' in '--__n'


-- 
           Summary: fill_n, generate_n assume Size is modifiable
           Product: gcc
           Version: 4.0.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sebor at roguewave dot com
 GCC build triplet: all
  GCC host triplet: all
GCC target triplet: all


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25306