[Bug c++/64611] New: Using a << operator inside an overloaded << operator gives compile error

[jvoosten at bankai dot nl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64611

            Bug ID: 64611
           Summary: Using a << operator inside an overloaded << operator
                    gives compile error
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jvoosten at bankai dot nl

Created attachment 34453
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34453&action=edit
Preprocessed file

The following code gives a compile error on the indicated line:

#include <sstream>

class SmartStream
{
public:
    template <typename F> friend F &operator << (F &in, float f) 
    {
        in.type ("f");
        in.m_buf << f;          // This causes a 'recursive' compile call
        return in;
    }

protected:
    std::ostringstream m_buf;

    void type(const std::string &_type) {};
};


int main(int argc, char *argv[])
{
    SmartStream ss;
    ss << 123.456;
}


Compile output:

$ g++ -save-temps -c rec_stream.cpp -o rec_stream.o
rec_stream.cpp: In instantiation of 'F& operator<<(F&, float) [with F =
std::basic_ostringstream<char>]':
rec_stream.cpp:10:18:   required from 'F& operator<<(F&, float) [with F =
SmartStream]'
rec_stream.cpp:24:11:   required from here
rec_stream.cpp:9:9: error: 'class std::basic_ostringstream<char>' has no member
named 'type'
         in.type ("f");
         ^
rec_stream.cpp:10:18: error: 'class std::basic_ostringstream<char>' has no
member named 'm_buf'
         in.m_buf << f;          // This causes a 'recursive' compile call
                  ^


Basically, it's applying the friend operator << function on the internal
std::ostringstream object, while I would expect the compiler to pick
'std::ostringstream::operator <<()'. Furthermore, casting, using :: resolution
operators, using the 'using' word all does not work. In fact, even the
following still triggers the error:


template <typename G>
std::string xyz(std::ostringstream &buf, G _param)
{
    buf.str("");
    buf << _param;
    return buf.str();
}

..and replacing the offending line with

  xyz<float>(m_buf, f);


Only if I move the code completely outside of SmartStream in a separate
function it will compile.

I also posted this on StackOverflow
(http://stackoverflow.com/questions/27952591/using-a-operator-inside-an-overloaded-operator)
and apparently this compiles on clang++. Perhaps there's an ambiguity towards
which 'operator <<' must be applied, but then I'd expect to be able to specify
which one.