Public bug reported:
The following does not compile with 5.2.1 (20150825) and 6.0.0 (20150825).
Ok with 4.9.3 and clang++ (3.5 and 3.6).
#include <array>
#include <utility>
struct Pos
{
unsigned l,c,a;
//fix g++
// constexpr Pos(unsigned l, unsigned c, unsigned a)
// : l(l), c(c), a(a)
// {}
};
template<class T, T... Ints>
constexpr std::array<Pos, 9*9> make_grid_position(std::integer_sequence<T,
Ints...>)
{
return std::array<Pos, 9*9>{Pos{Ints / 9, Ints % 9, (Ints / 9) / 3 * 3 +
(Ints % 9) / 3}...};
}
constexpr std::array<Pos, 9*9> make_grid_positions()
{
return make_grid_position(std::make_index_sequence<9*9>{});
}
template<class T>
void generate_sudoku(T)
{
constexpr std::array<Pos, 9*9> positions = make_grid_positions(); // fail
}
int main()
{
constexpr std::array<Pos, 9*9> positions = make_grid_positions(); // ok
generate_sudoku(1);
}
error:
std::array<Pos, 81ul>{std::__array_traits<Pos, 81ul>::_Type{Pos{0u, 0u, 0u},
Pos{0u, 1u, 0u}, Pos{0u, 2u, 0u}, Pos{0u, 3u, 1u}, Pos{0u, 4u, 1u}, Pos{0u, 5u,
1u}, Pos{0u, 6u, 2u}, Pos{0u, 7u, 2u}, Pos{0u, 8u, 2u}, Pos{1u, 0u, 0u},
Pos{1u, 1u, 0u}, Pos{1u, 2u, 0u}, Pos{1u, 3u, 1u}, Pos{1u, 4u, 1u}, Pos{1u, 5u,
1u}, Pos{1u, 6u, 2u}, Pos{1u, 7u, 2u}, Pos{1u, 8u, 2u}, Pos{2u, 0u, 0u},
Pos{2u, 1u, 0u}, Pos{2u, 2u, 0u}, Pos{2u, 3u, 1u}, Pos{2u, 4u, 1u}, Pos{2u, 5u,
1u}, Pos{2u, 6u, 2u}, Pos{2u, 7u, 2u}, Pos{2u, 8u, 2u}, Pos{3u, 0u, 3u},
Pos{3u, 1u, 3u}, Pos{3u, 2u, 3u}, Pos{3u, 3u, 4u}, Pos{3u, 4u, 4u}, Pos{3u, 5u,
4u}, Pos{3u, 6u, 5u}, Pos{3u, 7u, 5u}, Pos{3u, 8u, 5u}, Pos{4u, 0u, 3u},
Pos{4u, 1u, 3u}, Pos{4u, 2u, 3u}, Pos{4u, 3u, 4u}, Pos{4u, 4u, 4u}, Pos{4u, 5u,
4u}, Pos{4u, 6u, 5u}, Pos{4u, 7u, 5u}, Pos{4u, 8u, 5u}, Pos{5u, 0u, 3u},
Pos{5u, 1u, 3u}, Pos{5u, 2u, 3u}, Pos{5u, 3u, 4u}, Pos{5u, 4u, 4u}, Pos{5u, 5u,
4u}, Pos{5u, 6u, 5u}, Pos{5u, 7u, 5u}, Pos{5u, 8u, 5u}, Pos{6u, 0u, 6u},
Pos{6u, 1u, 6u}, Pos{6u, 2u, 6u}, Pos{6u, 3u, 7u}, Pos{6u, 4u, 7u}, Pos{6u, 5u,
7u}, Pos{6u, 6u, 8u}, Pos{6u, 7u, 8u}, Pos{6u, 8u, 8u}, Pos{7u, 0u, 6u},
Pos{7u, 1u, 6u}, Pos{7u, 2u, 6u}, Pos{7u, 3u, 7u}, Pos{7u, 4u, 7u}, Pos{7u, 5u,
7u}, Pos{7u, 6u, 8u}, Pos{7u, 7u, 8u}, Pos{7u, 8u, 8u}, Pos{8u, 0u, 6u},
Pos{8u, 1u, 6u}, Pos{8u, 2u, 6u}, Pos{8u, 3u, 7u}, Pos{8u, 4u, 7u}, Pos{8u, 5u,
7u}, Pos{8u, 6u, 8u}, Pos{8u, 7u, 8u}, Pos{8u, 8u, 8u}}}’ is not a constant
expression
If generate_sudoku isn't a template, it compiles.
g++-5 -std=c++14 -v
Using built-in specs.
COLLECT_GCC=g++-5
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 5.2.1-15ubuntu5'
--with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-5 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 5.2.1 20150825 (Ubuntu 5.2.1-15ubuntu5)
** Affects: gcc-5 (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1491643
Title:
Construction failure of a POD through a constexpr function if called
in a template function
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