[Bug c++/60245] New: Template static function not accepted as constexpr parameter

["florent.hivert at lri dot fr" <gcc-bugzilla@gcc.gnu.org>]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60245

            Bug ID: 60245
           Summary: Template static  function not accepted as constexpr
                    parameter
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: florent.hivert at lri dot fr

GCC is not able to compile the following code

#include <array>

using Ar = std::array<unsigned long, 10>;

template<typename T>
constexpr T Apply(const T& in, T (*f)(const T&)) { return f(in); }

static constexpr Ar id(const Ar& line) { return line; }
static constexpr Ar ar1 = {{1}};
static constexpr Ar results1 = Apply<Ar>(ar1, &id);

It complains that 

bug4.cpp:10:50:   in constexpr expansion of ‘Apply<std::array<long unsigned
int, 10ul> >((* & ar1), id)’
bug4.cpp:6:63: error: expression ‘id’ does not designate a constexpr function
 constexpr T Apply(const T& in, T (*f)(const T&)) { return f(in); }

This seems to be a problem with template substitution since manually
specializing the template makes the error vanish:

#include <array>

using Ar = std::array<unsigned long, 10>;

template<typename T>
constexpr T Apply(const T& in, T (*f)(const T&)) { return f(in); }

// manual specialization:
template<>
constexpr Ar Apply<Ar>(const Ar& in, Ar (*f)(const Ar&)) { return f(in); }

static constexpr Ar id(const Ar& line) { return line; }
static constexpr Ar ar1 = {{1}};
static constexpr Ar results1 = Apply<Ar>(ar1, &id);


System informations:

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib64/gcc/x86_64-suse-linux/4.8/lto-wrapper
Target: x86_64-suse-linux
Configured with: ../configure --prefix=/usr --infodir=/usr/share/info
--mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64
--enable-languages=c,c++,objc,fortran,obj-c++,java,ada
--enable-checking=release --with-gxx-include-dir=/usr/include/c++/4.8
--enable-ssp --disable-libssp --disable-plugin
--with-bugurl=http://bugs.opensuse.org/ --with-pkgversion='SUSE Linux'
--disable-libgcj --disable-libmudflap --with-slibdir=/lib64 --with-system-zlib
--enable-__cxa_atexit --enable-libstdcxx-allocator=new --disable-libstdcxx-pch
--enable-version-specific-runtime-libs --enable-linker-build-id
--program-suffix=-4.8 --enable-linux-futex --without-system-libunwind
--with-arch-32=i586 --with-tune=generic --build=x86_64-suse-linux
Thread model: posix
gcc version 4.8.1 20130909 [gcc-4_8-branch revision 202388] (SUSE Linux)
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From: "florent.hivert at lri dot fr" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/60245] Template static  function not accepted as constexpr parameter
Date: Mon, 17 Feb 2014 16:47:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`245

--- Comment #1 from Florent Hivert <florent.hivert at lri dot fr> ---
Created attachment 32155
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id2155&actioníit
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