[英]Variadic template metaprogramming : a bug in clang++ or g++?
Consider this variadic template madness to cast an array from one type to another: 考虑这种可变参数模板疯狂将数组从一种类型转换为另一种类型:
#include <array>
#include <type_traits>
template <typename Type>
class Converter
{
public:
template <typename OtherType, unsigned int OtherSize, class Array, typename... Types, class = typename std::enable_if<sizeof...(Types) != OtherSize>::type>
static constexpr const std::array<OtherType, OtherSize> convert(const Array source, const Types&... values);
template <typename OtherType, unsigned int OtherSize, class Array, typename... Types, class = typename std::enable_if<sizeof...(Types) == OtherSize>::type>
static constexpr const std::array<OtherType, OtherSize> convert(const Array, const Types... values);
};
template <typename Type>
template <typename OtherType, unsigned int OtherSize, class Array, typename... Types, class>
constexpr const std::array<OtherType, OtherSize> Converter<Type>::convert(const Array source, const Types&... values)
{
return convert<OtherType, OtherSize>(source, values..., OtherType(source[sizeof...(values)]));
}
template <typename Type>
template <typename OtherType, unsigned int OtherSize, class Array, typename... Types, class>
constexpr const std::array<OtherType, OtherSize> Converter<Type>::convert(const Array, const Types... values)
{
return std::array<OtherType, OtherSize>({{values...}});
}
int main(int argc, char* argv[])
{
Converter<double>::convert<int, 3>(std::array<double, 3>({{1., 2., 3.}}));
return 0;
}
This code compiles well under g++4.7 and g++4.8 but not under clang++3.2 : 这段代码在g ++ 4.7和g ++ 4.8下编译得很好,但在clang ++ 3.2下却没有编译:
main.cpp:16:67: error: conflicting types for 'convert'
constexpr const std::array<OtherType, OtherSize> Converter<Type>::convert(const Array source, const Types&... values)
^
main.cpp:9:65: note: previous declaration is here
static constexpr const std::array<OtherType, OtherSize> convert(const Array source, const Types&... values);
^
main.cpp:23:67: error: conflicting types for 'convert'
constexpr const std::array<OtherType, OtherSize> Converter<Type>::convert(const Array, const Types... values)
^
main.cpp:11:65: note: previous declaration is here
static constexpr const std::array<OtherType, OtherSize> convert(const Array, const Types... values);
Is g++ too permissive or is it a bug in clang++ (and if so, is there a public bugtracker of clang++) ? g ++是否过于宽松,或者它是clang ++中的错误(如果是这样,是否存在clang ++的公共错误跟踪器)?
是的,这就是已经在clang和修复中报告的这个bug 。
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