http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57846
Bug ID: 57846
Summary: CRTP, templates, metaprogramming, forwarding and
static member
Product: gcc
Version: 4.8.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vince.rev at gmail dot com
This code (I could not find a simpler example) does not compile under g++ for
some obscure reasons (tested with 4.8.1 and 4.7.2) (see the related discussion
on stack overflow here :
http://stackoverflow.com/questions/17515079/crtp-templates-metaprogramming-forwarding-and-static-member-a-bug-in-g-4-8):
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#include <iostream>
#include <type_traits>
#include <utility>
#include <tuple>
#include <array>
template <class Crtp, class... Types> struct Base
{
template <unsigned int Index, class Type = typename
std::tuple_element<Index, std::tuple<Types...> >::type> inline const Type&
get() const {return std::get<Index>(data);}
template <unsigned int Index, class Type = typename
std::tuple_element<Index, std::tuple<Types...> >::type> inline Crtp& set(const
Type& value) {std::get<Index>(data) = value; return static_cast<Crtp&>(*this);}
std::tuple<Types...> data;
};
template <typename Type, unsigned int Size> struct Derived : public
Base<Derived<Type, Size>, std::array<Type, Size>>
{
template <class... Args, class Template = decltype(std::declval<const
Base<Derived<Type, Size>, std::array<Type, Size>>>().template
get<0>(std::declval<Args>()...))> inline Template test(Args&&... args) const
{return this->template get<0>(std::forward<Args>(args)...);}
template <class... Args, class Template = decltype(std::declval<const
Base<Derived<Type, Size>, std::array<Type, Size>>>().template
set<0>(std::declval<Args>()...))> inline Derived<Type, Size>& test(Args&&...
args) {return this->template set<0>(std::forward<Args>(args)...);}
static void check() {Derived<double, 3> derived;
std::cout<<derived.test()[0]<<std::endl;}
};
int main(int argc, char* argv[])
{
Derived<double, 3> derived; std::cout<<derived.test()[0]<<std::endl; //
Working
Derived<double, 3>::check(); // Not working: error: no match for
‘operator[]’ (operand types are ‘Derived<double, 3u>’ and ‘int’)
return 0;
}
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