http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53497
Bug #: 53497
Summary: Partial ordering of function templates does not order
lvalue/rvalue references correctly
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: vlu...@gmx.de
Following defect report 1164
(http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1164) a rule was
added to partial ordering of function templates, so that parameters declared as
lvalue-references are considered more specialized than those declared as
rvalue-references. GCC does not implement this, i.e.
-----------------------------------------------
template<typename T>
void t(T&);
template<typename T>
void t(T&&);
int x;
void f() {
t(x);
}
-----------------------------------------------
is rejected by GCC 4.7.0 and a 4.8.0 prerelease. Diagnostic for the latter is:
---------------------------------------------------------------------
c++ -std=c++11 -c ref_binding.cc
ref_binding.cc: In function ‘void f()’:
ref_binding.cc:8:6: error: call of overloaded ‘t(int&)’ is ambiguous
t(x);
^
ref_binding.cc:8:6: note: candidates are:
ref_binding.cc:2:6: note: void t(T&) [with T = int]
void t(T&);
^
ref_binding.cc:4:6: note: void t(T&&) [with T = int&]
void t(T&&);
^
---------------------------------------------------------------------
Full compiler identification:
---------------------------------------------------------------------
c++ -v
Using built-in specs.
COLLECT_GCC=/home/lima/vanilla_installs/gcc_and_tools/bin/c++
COLLECT_LTO_WRAPPER=/home/lima/vanilla_installs/gcc_and_tools/lib/gcc/x86_64-unknown-linux-gnu/4.8.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc_svn/configure
--prefix=/home/lima/vanilla_installs/gcc_and_tools --enable-threads
--enable-__cxa_atexit --enable-languages=c,c++
--enable-version-specific-runtime-libs --disable-multilib
Thread model: posix
gcc version 4.8.0 20120526 (experimental) (GCC)
--------------------------------------------------------------------
DR 1164 appears to have made it into the standard, it is marked FDIS and I find
it in both the N3290 and N3376 drafts of C++.
