http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56215
Bug #: 56215
Summary: Cannot create constexpr struct with unnamed unions
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: t-gcc-bugzi...@snowelm.com
Similar to PR c++/51675, but the trunk GCC fails to compile the following code:
------
struct foo {
union
{
int x;
short y;
};
constexpr foo() : x( 0 ) { }
};
------
$ g++ --std=c++11 hoge.cpp
hoge.cpp: In constructor ‘constexpr foo::foo()’:
hoge.cpp:7:33: error: uninitialized member ‘foo::<anonymous>’ in ‘constexpr’
constructor
constexpr foo() : x( 0 ) { }
^
What I actually want to do is a specialization of std::pair to provide
efficient comparison. Since this requires an unnamed struct within an unnamed
union, and
the bug seems very sensitive to details like that, I put the code too.
GCC trunk also fails compiling the following.
------
#include <utility>
#include <cstdint>
namespace std {
template <>
struct pair< uint32_t, uint32_t > {
union
{
struct {
uint32_t first;
uint32_t second;
};
uint64_t paired;
};
constexpr pair() : paired( ) { }
constexpr pair(uint32_t a, uint32_t b) : first(a), second(b) { }
};
constexpr bool operator==
( pair<uint32_t,uint32_t> a, pair<uint32_t,uint32_t> b )
{
return a.paired == b.paired;
}
constexpr bool operator<
( pair<uint32_t,uint32_t> a, pair<uint32_t,uint32_t> b )
{ // only for little endian
return ((a.paired<<32)|(a.paired>>32)) < ((b.paired<<32)|(b.paired>>32));
}
} // namespace
std::pair<uint32_t,uint32_t> x(1, 2);
------
