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From: "akim.demaille at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/53540] New: C++11: using fails to be equivalent to typedef
Date: Thu, 31 May 2012 14:44:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53540

             Bug #: 53540
           Summary: C++11: using fails to be equivalent to typedef
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: akim.demaille@gmail.com


Created attachment 27532
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27532
test case

Hi all,

I hope this is not a bogus bug report, I apologize if there is something I
misunderstood.  I observed the following with both 4.7.0 and "4.8":

g++-mp-4.7 (MacPorts gcc47 4.7.0_3) 4.7.0
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

g++-mp-4.8 (MacPorts gcc48 4.8-20120527_1) 4.8.0 20120527 (experimental)
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

In the following example, I import a type name from a templates struct with
"using", and do the same with "typedef".  The latter works, but "using" does
not seem to find the definition.  clang finds it though (but then again, my
understanding might be wrong).

If "function" is not templated, there is no problem.


$ cat foo.cc
template <typename T>
struct context
{
  typedef int type;
};

template <typename T>
void function()
{
  using ctx1 = context<T>;
  typename ctx1::type f1;

  typedef context<T> ctx2;
  typename ctx2::type f2;
}

int main()
{
  function<int>();
}


$ g++-mp-4.8 -Wall -std=c++11 foo.cc
foo.cc: In instantiation of 'void function() [with T = int]':
foo.cc:19:17:   required from here
foo.cc:11:23: error: no type named 'type' in 'using ctx1 = struct context<T>'
   typename ctx1::type f1;
                       ^
foo.cc:14:23: warning: unused variable 'f2' [-Wunused-variable]
   typename ctx2::type f2;
                       ^